I've been playing some BF3 on my 2008 gaming rig and It is clear I need to upgrade. on low quality it is playable but I hit stutters and think that my experience is suffering. I don't want to do a full rebuild, so I'd like suggestions to upgrade. Any chance I could just pop in a 560 Ti and all would be good?
Operating System: Windows 7 Home Premium 64-bit (6.1, Build 7601) Service Pack 1 (7601.win7sp1_gdr.110622-1506)
System Manufacturer: Gigabyte Technology Co., Ltd.
System Model: EP35-DS3L
BIOS: Award Modular BIOS v6.00PG
Processor: Intel(R) Core(TM)2 Extreme CPU X9650 @ 3.00GHz (4 CPUs), ~2.7GHz
Memory: 4096MB RAM
Available OS Memory: 4094MB RAM
Page File: 5408MB used, 3649MB available
DirectX Version: DirectX 11
DWM DPI Scaling: Disabled
BFG Tech BFGR88768GTXE GeForce 8800 GTX 768MB 384-bit GDDR3 PCI Express x16 HDCP Ready SLI Support HDCP Video Card
Speakers (Creative SB Audigy 4 (WDM))
Thermaltake Armor Series VA8000BWS Black Aluminum / Steel ATX Full Tower Computer Case
ZALMAN CNPS9700 LED 110mm 2 Ball CPU Cooler
CORSAIR DOMINATOR 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) Dual Channel Kit Desktop Memory Model TWIN2X4096-8500C5DF
PC Power & Cooling Silencer 750 EPS12V 750W EPS12V SLI Certified CrossFire Ready Active PFC Power Supply
A PCI-e 2.0 card will fall back onto PCI-e 1.x standard with backward compatibility, so it wouldn't be an issue if you plug a GTX 560 into your motherboard. I think it might be bottlenecked somewhat due to less bandwidth, though I can't be sure how severe it might be.
I cannot really see anything in your current build that has to go apart from the gfx card.
Seeing as you had a 8800GTX, a GTX 560Ti that you wrote about in your OP will see a huge improvement in gaming performance over your current set up. The rest of your specs are plenty good. You don't really need any more upgrades as of now.
But on your resolution, the 570 will come with a bit of future proofing.
2MB cards are becoming more prevelent lately. Usually due to multi monitor setups or single monitors with 25xx X 16xx resolutions. The GDDR memory is solely used for frame buffers. The amount of GDDR memory above 1GB is mostly unused with 19xx X 10xx and lower resolution displays. But if you can afford it, go for the extra memory for future proofing.