What will more RAM do in a system that already has 4Gb? Probably not much, Lenny....and for those that are suggesting you shave off a few bits from your current component list to afford a better graphics card: If he "shaves off" any more than he already has, he won't have much IMO.
Lenny, you're already using some of the best "bang for buck" equipment available out there. But if you can afford a BIT better graphics card than a GTX 550Ti, then by all means GET IT. Also, keep this in mind:
The average GTX 550Ti retails for between $130 and $150 USD...it's entirely possible to get something a generation older and more powerful while staying within that price range. For example, right now there's a PNY GTX 460 (1GB) at Newegg.com which is more powerful than the GTX 550Ti for the same price and will work well on your intended system.
The only thing that you should keep in mind is, that the GTX 460 comes in two "flavors" and will consume about 60 more watts than the GTX 550Ti. First, get the 1gb version and second, your 650 watt PSU will be more then enough for either card.
Best wishes.
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System Specs:
Intel i5-2500K
GA-Z68XP-UD3
GTX 560Ti
8gb G.Skill DDR3 1600
Antec 750W
SoundBlaster X-Fi Titanium
Corsair F60 SSD
Windows 7 64-bit
CH Fighterstick, Pro Pedals