Is this a good ram/cpu upgrade?

I've got an Asus A7N8X, XP2100 cpu, 512k PC2700 ram + Geforce 6800GT. Obvious huge bottleneck for that video card. I plan on getting an XP3000 cpu + 512k PC3200 ram. Can I run the PC3200 with the PC2700 for now until I can replace the one PC2700 stick with another PC3200? How much of a performance difference is there at PC2700 speeds vs. PC3200? I don't plan on overclocking right now.

Really should try the OC. This is after all ocforums! Most PC-2700 wil oc to PC-3200 quite easilly, and your 2100+, assuming that it's a tbred-b is good to at least 2.2ghz if not more. My old 2100+ ran 2.4ghz stable 24/7. You should invest in another 512 stick of ram as you will notice a the difference in games like farcry and doom3, and maybe invest in a more OC friendly mobo and HSF. In short, an XP @ 2.4 ghz 1:1 fsb @ a minimum of 400mhz(200mhz in BIOS) and a gig of ram should would be better a "bang for the buck" then a new a XP3000+.

My chip is a Palamino I think, not t-bred so it won't overclock much anyway.

Yes you can run pc3200 with pc2700 but you will probably have to run at pc2700 speeds. Most of the Barton cores run at 333mhz, but some of them are meant to run at 400mhz. I'd recommend keeping your rig until you can get the CPU and PC3200 all at once.

The bottleneck on AMD XP cpus is in the memory bandwidth. The difference between running your FSB/RAM at 400mhz and 333mhz can be pretty big.

Also, having a gig of memory at pc2700 versus 512mb at pc3200 sucks. Stepping up to a gig then downgrading back to 512mb might not be something you enjoy.

Perhaps you should consider upgrading your CPU to a Barton that runs at 333mhz and just buying another 512 of PC2700. You might be happier with that.