The "keep old stuff" option (most GPU power):
If you've got room on the mobo, add some RAM to get to 8GB total (a 2x2GB set is
$50 right now on Newegg at least). Sell that old graphics card; you can get $60-70 for it at least.
If that motherboard can overclock, DO SO. It will add life to that old sucker. Follow
this guide. Basically, kick the FSB to whatever your RAM is rated for divided by four.
If all has gone well, you'll have a substantially higher clocked CPU and spent little money out of pocket. Get a 7950 (
$300) with the remaining money.
Alternatively (the no overclock now/least GPU power option):
Sell the old stuff on the FS/FT forum. If the motherboard is sufficiently good, you can get $200 or more out of the deal (we are talking about old tech; a E6600 sells for $90 or so). Your budget is now effective $550.
Buy an Asus P8Z77V-LK and i5-3570K (this will overclock if you want it in the future, so long as you get a $30 or so cooler) for $300 as a
combo. Get a 2GB version of the 7850 for
$180 ($170 AR). Get 2x4GB of DDR3 RAM for
about $50 (with the code provided on the page).
Another alternative (absolutely no overclocking ever! Plus, nearly as much GPU power as the first option!):
Sell the old stuff, as before, and hopefully get $200 or so. Get an i5-3350P for
$180 and a Biostar B75MU3+ for
$70. Then get a 7870XT (
$250) and 2x4GB of DDR3 RAM (
$50).
Some notes about each option:
On the CPU side: The E6600 at stock will cut your framerate by a third or so in modern games, especially at a lower resolution (like 1650x1050). Overclocking it will allow you to reduce that penalty to about 15-25%, depending on the game. Whatever modern option you get will work well, but the 3570K will have a bit more long term power because it can easily overclock about 25%.
On the GPU side: The 7850 can easily handle modern 1080p games at high, so it should handle games within the next year equally well at 1650x1050. The 7870XT and 7950 will be good for extra eye candy, and they'll have more longevity.
