just saw the benchmarks on that site, the Ti4200 does bloody well, considering its age, and the game it is being tested in!
if the motherboard runs 2 sticks in dual channel, 3 will be slower. since socket 754 doesn't support dual channel, 3 sticks will not be slower than 2
corsair XMS RAM isn't that much of a difference to value RAM in real perforrmance, but XL RAM really takes off, and outperforms PC4000 memory
if you want to spend the money on faster RAM, PC3200XL is the way to go, otherwise you will still get good performance with 2 sticks of Kingston value