It's primarily for games, but I also kinda wanted it for MAX too.
For modern games the video card(s) are king, so you'll get the most out of your money by going heavy on that and skimping on pretty much everything else, but 3D rendering on the other hand is entirely processor dependent. Also, note that SLI is really only suitable for modern games due to issues with vsync, although it shines in those games, so if you play older games make sure that one card by itself is fast enough at the settings you want.
Also, 32-bit XP will only be able to use 3.2GB (or something around there) of the memory, so you will need to use something else in programs where you want to use of the full 4GB.
I bought 2x1GB of G.Skill HZ memory from overclockers.co.uk yesterday. It should overclock very nicely; it uses Samsung's UCCC chips, which are the higher capacity versions of the TCCD/TCC5 chips overclockers worldwide know and love. They can reach insane clock speeds at fairly low voltages, but the latencies can need to be as high as 3-4-4-10 at 270MHz.
BTW, is that rig going to be watercooled? X2s do run quite cool anyway but I'm wondering how far I can push my 4200+ since it usually runs at around 30 degrees C (with fans off) in FEAR or Doom 3.
I'm thinking of getting those sticks myself, as they are only about $15 more than value memory. Although the high timings generally negate the effect of the bandwidth, so the G.Skill 2-3-2 sticks for the same price may be a better option. I don't really need 2GB at the moment but I could use some memory for a second computer, so I might as well transfer my existing 1GB pack to that and switch the main system to some 2GB pack.
As for the 4200, most of the Manchesters do 2.5-2.7ghz on good air cooling, although you can afford to take the vcore a bit higher due to the watercooling. I think most of these A64s aren't really limited by the temperature though, except maybe some of the 2x1MB dual cores and FXs. I can get a stable 3ghz with 1.52V on a single core 146 with just an XP90.
I can still use mouses, but they're rather annoying (pain in the right shoulder, if I use them too often.
I just keep my sensitivity cranked up, so I rarely need to move my wrist/arm at all, which I think is what can cause the pain.