I personally went with another 8800gt for sli in my rig. Im gonna try to get atleast another year+ out of my rig. Now that depends if your motherboard supports sli. If not I personally would go for the 4870 or the 260 gtx.
Don't bother with MB Ram just get another 8800GT for sli and you will have 4870/GTX260 perfomance. Don't bother with an upgrade from that CPU/MB until after I7 launch. 775 could see massive price reduction/ I7 might own everything surrently available
I am actually planning on keeping my 8800GT the way it is for now.
I can play COD4 and every other game @ 1920x1200 MAX settings (except for Crysis/Warhead).
I did actually think long and hard about this.
So, if you have a 1920x1200 screen and want to play Crysis @ MAX settings, you need a card with unearthy performance. Even the 4870 X2 isn't 100% smooth at that setting (may drop below 30fps sometimes).
So, if your monitor is smaller than 1920x1200, keep your 8800GT and save some cash. Your p45 is plenty good enough for now. Any C2D is fast enough for any game for now.
I personally played Crysis @ 1680x1050 on high-settings smoothly enough.
When DX11 gets released, you should get a quad-core CPU; maybe a q9550. That and a high-end card in late 2009 should keep your rig current for a a few years.
Also have 4+ gigs RAM if you have Vista 64. RAM is a cheap way to get speed (another topic)
Well I guess if you want the best possible gaming then yeah with games like FC2 and Crysis you maybe able to take advantage of the 4 cores but most games out there don't require 4 cores so I'd rather you get a Dual core but OC it. You will get pretty close to 4 core performance in most games while paying less.
For graphics card 8800gt does the job for most resolutions. I've tried Crysis DX9 on 8800GT under 1028 x 1024 and 1680 x 1050 and both are producing playable frames (I applied Natural mod and shader mod). I've gotten around average of 30 - 40 fps and a high of 50ish Fps. It's still a very good card. I haven't lagged one bit during crysis game play and I have it set to 0xAA, Very High settings. Without the natural and shader mod I have it running at around 30 frames - 35 frames. It's pretty decent still.
But for sure if you want a good card and future proof it a little for up coming titles 4870 is no doubt the card to go with. I have 4870 1GB card. Running crysis in XP (Dx9) I have it at 30min, 35 avg and 40 fps high under Very High settings, 2x AA on 1680 x 1050 resolution. This is very stunning for results (8800gt would've dipped to non-playable by now). Game play is smooth and I did not notice much lag. I'm on Cataylst 8.10.
These are just some of my personal experiences that you can take into consideration when choosing a video card.