I don't have any problems with FPS or anything like that on what I'm running currently...just wanted to see if I can get a few more FPS, if possible, from games that do support CrossfireX or be able to turn up a couple graphic level details to their highest settings in certain games. Most of the info that I've read so far seems to point that I'll see more benefits from it as a single-display user than a multi-display user would, at least in the programs I'm running. And, if it doesn't work or I don't see a worthy gain in performance or the headaches with it get too bad, I can always go back to a single card configuration that's not given me any problems.

I was looking at upgrading...probably for the sake of upgrading as much as anything...and it looks like I'd have to pay $400 to gain any significant performance increases over my current card, according to the majority of benchmarks I've seen. If for a quarter of that price an identical card like I'm running gives me the same performance increase, which seems to only be 10% or so according to benchmark tests, as a $250-300 one...I figure it's worth a try.

I imagine it's going to be a learning experience if nothing else.

Yeah sounds like you are approaching it with your eyes open, if the games you play most support crossfire and your current card works ok with the others then indeed it's a decent bang for the buck especially for the prices of a second 5850 IMHO.

Man, SLI 670, that must be nice (assuming it works, lol). I'm likely going to buy a 4GB 670, though not until my life settles down a bit (and if I can possibly buy one used from a seller at someplace like Hardforum or Anandtech)

A Single 7950 OC would easily double your performance for traditional games, while accelerating DirectCompute programs tremendously

Probably about right -- more or less (depends on the game).

The HD7970 when overclocked (easy to do as stock clocks aren't jacked up as much as in GTX series) consistently tested better than GTX670 and GTX680 in high-pixel-count situations. That is, 30 inch high-res monitors and 3 monitor setups. Also tested better by far (more than twice as good) in compute applications -- that a few games are moving towards in the future. Lastly, Eyefinity 3 monitor has been around a while and is well supported.

So, since some folks are very particular, and since some folks already are concerned that FPS drops off significantly with three monitors, one could say that you can't get a single GPU solution for 3 monitors that's overkill, yet.

Most 3 monitor users have a big investment already (in monitors), so a few dollars more (like $50) to get the best possible 3 monitor performance would be well inside the budget.

Also note that GTX680 is not cheap being in the $500 plus range usually (HD7970 at under $500 usually is more cost effective, in general, for any application).

Just my usual verbose reasoning. More concisely, high-res gamers pay so much for monitors, they should not be put off by the price of one game extra for the a better 3 monitor GPU (comparing HD7970 to GTX670 -- and they save $$ compared to GTX680). On the other hand, the differences are not so great that one card or the other is a real mistake, in my opinion

Right now, the HD 7950's a bit out of my price range...the 7900's are something I'm looking at, but maybe later in the year or first of next year. I figure as far as "bang for the buck", it's going to be hard for me to beat adding another HD 5850 right now, for the price I've got this one at.

I've worn Google out, reading about CrossfireX and the pros and cons...also, the installation process and potential pitfalls that might arise. The opinions run from "it's actually slower" to "you won't see any increase" to "you'll see a 30% increase"...so I figure 10-15% is what to expect at the max overall.

What if the 7950 drop $50 in price?

@AnandTech

There's 7950s on NewEgg for $330 even lower after MiR, Free Shipping, 5 Egg Ratings, and 3 Free Games,

Which means you'd actually pay like $160 for the GPU if you factor in the package value:

MSI R7950 Twin Frozr 3GD5/OC Radeon HD 7950 3GB 384-bit GDDR5 PCI Express 3.0 x16 HDCP Ready CrossFireX Support Video Card
http://www.newegg.com/Product/Product.aspx?Item=N82E16814127667

Yeah latest GPU generation performance will always differ between different games, driver maturity, and the prices are an ever changing thing, currently per NewEgg they stacked in the following order based on lowest priced listed for each card just now:
GTX 680 - $499+ (no price drops yet since release, in fact price went up on most cards to $519)
HD 7970 - $439+ (multiple price drops since release)
GTX 670 - $399+ (no price drops yet since release)
HD 7950 - $339+ (multiple price drops since release)

Without taking overclocking into consideration (which I think depends a lot on the particular manufacturer, model and technical ability of the user), if I was recommending a video card I would say all 4 models are actually good triple monitor cards and they will bench within +- 10% of each other overall (that's a 5-6FPS difference on average at those resolutions) and provide acceptable framerate in triple monitor resolutions with a single card.

So IMHO I agree that comparing a 670 to a 7970 is a pretty arbitrary and personal thing where your own game preferences will be heavily weighed, I would suggest anyone making this decision research how the 4 cards perform on the particular games they are interested in, and what their bang/buck budget is on the particular day according to the current prices. This will keep changing as prices drop, drivers mature, new models come out so anything you or I recommend today will likely be redundant in 2 weeks time

As a long time triple monitor gamer, I'm just glad we reached the point where all the top and baby top current gen cards from both manufacturers support triple monitor on a single card so well, hopefully this will lead to more and more game/sim devs including native support without needing UI tweaks and workarounds to make the HUDS show up in the middle monitor.

I run two 5870's in Crossfire. Before that, I ran just a single 5870 for a year. I would say 1/3 of my games (Mainly the newer ones that could run in Eyefinity ie 3 monitors for me) saw an improvement. Those are:

Battlefield 3
Just Cause 2
LA Noir
Dead Island 2
DCS: A-10C Warthog
Call of Duty Black Ops
Call of Duty Modern Warfare 2
3DMark 2011
Heaven DX10/DX11 Benchmark

The rest of my games that only run on one monitor saw no real improvement. The other games I run on three screens but have some issues with Crossfire so I turn it off are:

Skyrim
Mafia II
Rise of Flight
DCS: Blackshark