GT 440 1GB DDR3>GT 240 1GB DDR3 and have DX11,but i suggest buy GTS 450 1GB DDR3~
Why a GTS450?
I know for a fact that the P4 will be easily bottlenecked by a 8800GT, let alone a GTS450. So spending more than required + new PSU isn't really worth it.
Best option is to find a HD5670 GDDR5 card. Those go for around $65, $15 less than a GT440 and offer a lot more performance.