I notice the card has 3GB of memory (which I assume adds to the cost). That amount only pays off at freakishly high resolutions (e.g. 30 inch monitor or 3 Monitors -- which may require two GTX580 with Nvidia).
I notice your monitor is 1680x1050. Typically, 1GB of memory is plenty up to 1920x1200. 1.5GB is good above 1920x1200. Most of that normally depends on the use of AA. If one does not use AA, memory above 1GB is less useful. For example, I have 5760x1200 Eyefinity. Though I use CrossFire, the "effective" memory is 1GB (as each card renders alternate frames). I don't normally use AA. But, I am in Skyrim -- along with virtually all the BIG texture mods. No problem.
I bring this up because you indicate the need for a card plus a hard drive and have a budget. If you are not going to up-size the monitor, you can easily get by with a 1.5GB memory GTX580 graphics card, I speculate -- this could save enough to afford the hard drive. Actually, for the size monitor you have, the GTX580 may be overkill (i.e. maybe consider GTX570).
FWIW.
_________________________
ATI Sapphire HD7970 OC - Eyefinity 5760x1200 24", 1xDell-U2410 H-IPS + 2xHP-ZR24w S-IPS, Extended 23" Samsung cPVA, Ceton InfiniTV 4, Bulldozer FX8150@4.5GHz w/Swiftech Water Cooling, 16GB GSKILL PC3 @1866, ASUS Sabertooth 990FX, Corsair 120GB SSD, WDigital + 3x Seagate + Hitachi + 2x WD Ext = 10.0TB, Sony DVD, OCZ ZX 850W PSU, CoolerMaster HAF922, TM Warthog HOTAS, TM T-Flight Stick X, TM Cougar+FSSB & CH Pedals, Saitek X52 Pro & Pro Combat Pedals, TrackIR5 w/TC Pro, Windows 7 HP 64b