You can never have too good of ram. Infact, you said your getting an nForce2 which from what I've seen and here can drive memory speeds of 600MHz+ (Seriously) without a single flaw. Although no memory module will ever be capable of 600MHz at least on standard DDR interface, it's a good thing to know that there is chipsets that can drive these insane speeds!
I see no reason why people wont venture to as high as 500MHz with Corsair PC3500 with very relaxed timings. For what the ram will loose in timings, it will definately make up for in MHz performance.
The AthlonXP 2800+ when it becomes available will be an excellent choice for running at or near 400MHz FSB. This way, you will get a vecious overclock while taking advantage of DDR400 and 400MHz FSB speeds. nForce2 will serve your CPU well.
So thats 200 X 13.5 = 2700MHz! This may be possible with a 2800+ CPU if your cooling with some nice copper or water!
EDIT: Even if you never achieve that overclock, the nForce2 allows multiple driving sets in MHz for the memory controller. This means that you can set your memory controller to do anywhere from -100% ~ +100% of the FSB.
EX: If your FSB is at 333MHz and you selected 25% ratio in the bios for the memory, then the memory would be running at 417MHz (25% more than 333).
OC-Master