can i upgrade my 8600GT

hello,

i run an old system

pentium 4 630 3,0ghz (stock) can overclock it to 3.46
asus p5ld2 mothterboard
2gigs of ram (4x512mb ddr2 533mhz)
asus geforce 8600GT

I bought the 8600GT past year in juli, i needed a card to upgrade my 6600GT. there weren't yet some threats and comments about the 8600GT, but after a month i started so see soms comments. and, i agreed with them all, that graka isn't a topper! i had an unnamed 400WATT psu, and when i bought the card, i got artifacts, so had had to buy a new one, 600 Watt silence (cheapest and sli ready), the artifacts were gone! but actually i didn't buy the GTS version because my psu had not an extra pin. but now i have with that new psu.

the diffrence between my 6600 an 8600 is that i can play the same games, at the same settings on an higher resolution with the same fps. example: battlefield 2142 at 55 fps on 1280X1024 res instead of 1024X768 at my 6600GT.

but, the thing is, i can play cod4 at decent settings and fps, but i want a better graphicscard. because when i play titanmaps on battlefield, my fps drops at 20 fps, and as all of you know, that's ennoying! but, i'm afraid if there will be more bottlenecks than i can suspect. the cpu is old...

here in Belgium you can get every card that exists!

but, i was thinking at the ati HD 3850 or a 8800GT or as it must a GS.

i guess the 3870 and 8800GT would be to heavy

but the 3850 would it be usefull to change, or will my cpu be a bottleneck and the fps wouldn't change at all?

and is there an 512mb version of this card?
or is the best option, to wait untill i want to buy an new system to play bf 3 in the future?

greetings, and i hope you will give me some advise!

Vochtige