Well, you know that you should expect that Vista is going to run games
roughly 5-10% slower than XP. In some games my numbers are around 15-20%
(namely Doom3), but that might be resolved with later drivers for my card.
1.5GB is a pretty good amount of ram to have. I play BF2, BF2142 and FEAR.
Those last two can munch on some ram. But the most I've seen either use is
1.3GB-1.4GB and that's under Vista.
Also, they are working on a HL2 64bit and I ran the benchmark and it's
40-50fps slower than running the 32bit version. One response I got on the
Steam forums is that 64bit code is substantially slower than 32bit code. I
don't know how true that is and google searches haven't yielded a clear
answer. So if you're thinking going to 4GB and\or 64bit windows is going to
make things better it may not.
If you search this newsgroup, you'll see a thread about BF2 doing excessive
swapping which leads to choppy play. I also get that choppy play, but it's
has nothing to do with the amount of ram I had, as I had 600MB free when it
start doing whatever it was doing.
I'm sure it's in your plans, but instead of the extra ram, I'd be looking to
spend that money on a new video card. The 5700 is getting fairly long in the
tooth. For about the same amount of money you're spending on RAM and a
motherboard, you could get like a 7600GT.
I'm guessing that you're wanting to move to a PCI-e board, so you might be
upgrading anyways. but I would say, try it with 2GB first and then add more
later. Unless you just want to have 4GB of ram. Most systems only report 3GB
under windows, 1Gb is set aside for the hardware or something to that effect