Upgrading my Pentium-D. Right move, wrong move?

Redheadsrule13

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Oct 25, 2013
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I have a lower end PC which I want to be able to game on with reasonable performance. I'm trying to run BF3, but my framerate is still jittery even at lowest settings (including res). I know my graphics card is good enough, but I think the big bottleneck here is my motherboard and CPU. I'm thinking of replacing them next. What do you guys think? What should I upgrade to in order to stop bottlenecking my 640 while keeping the price point as low as possible?
(Also: I know I need a better PSU, but I should be getting a 1000 watt one second-hand soon.)

Full system specs:
Current GPU: Galaxy GT 640
CPU: Intel Pentium-D 930
RAM: 4GB DDR2 667MHZ
Motherboard: Dell WG864 (http://www.redplanettrading.com/Dell-WG864-0WG864-Mothe...)
PSU: 300watt (Whatever comes with the Dell Dimension E520 system)
HDD: 7200RPM Western Digital 200GB
OS: Win 7 Ultimate 64bit
 
definitely, get a new pc.

your cpu is old, probably hot too (i've heard of temp issues, a lot)
and i don't think there is a bottleneck here, gt640 is not fast. If this was a 650, then maybe most things on low to have a stable fps.
i used to have a 560Ti playing bf3, mostly set to med (with 1 or 2 high) just to have stable (>50) fps

so, if it was me, ill save up and get a new one. even if you buy an i7, with that 640, it will still be slow