Do I have to upgrade my CPU to support 260 GTX?

Is your board a socket 939? If so I'd say go for a full upgrade as it will severely bottleneck anything over the 8800GT.

The board is AM2. (M57SLI-S4 (MPS ver. 1.4) nForce N51 MCP)
I understand that installing the 260 on 4600+ is not the best configuration.
The question is: if installing 260 instead of 8600 GTS will give me a boost of say 200% instead of 250% theoretical - than I'm fine with this and upgrade the CPU later.

What do You think?

Depands:
on middle settings in Fallout3 I get about 30-40 fps
but in overlord 2 the situation is worth - don't know the exact fps but I'd say about 15-25.

I dont remember the exact settings, but I think it's with the standart game settings - I didn't change that.

Ok I'll try that.
Thanks!

I have the following configuration:
Athlon 64 X2 5000+
4gb of 666mhz ram
Graphics: Just recently got a GTX 260

Overall I saw a huge improvement over my 9400gt, Fallout 3 goes at max settings in the 50 fps ranges, same with Overlord 2, COD 4 and Lost Planet, all at 1920x1080. A while back I posted about a potential bottleneck in my system, and the general answer was that my cpu wasn't fast enough to fulfill the gtx 260 So I would say you would see a great boost in performance until you can upgrade your processor, I'm still waiting to upgrade my motherboard to an AM3 socket to support a quad core.

Honestly save up and just upgrade to a new rig; unless you can overclock your current system. 2.7ghz+ cpu and 400mhz+ memory. With your current rig get a gts250/4850 anything above would be a waste of money.

gts250: http://www.newegg.com/Product/Product.aspx?Item=N82E168... ($95)

4850: http://www.newegg.com/Product/Product.aspx?Item=N82E168... ($90)

What a load of Tosh.... although CPU bottlenecks DO exist this only appears to be a problem at Lower resolutions at which point your GPU isnt going to be maxxed out anyway.

As long as your stressing your card more than the CPU you should be fine. Ie. play at Full HD resolutions. @ 1440 x 900 its probably slightly overkill anyway with a gtx 260 for this generation of games (except crysis). But going down the gtx260 route will futureproof your rig for atleast a yr or so until you have to tuen down the detail settings to play the new games.

Listen to Invisk, take his advice. Anything over those two recommended cards would be a waste of your money. In the future if you upgrade the CPU with the GTX 260, if that's what you were to buy, a much faster GPU would be for much less. Spend under $100 and you'll be fine.