I am not a P4 Pro, but I do have a couple A64 systems. The A64 in not very sensitive to tight timings like the P4 or XP. Not saying that they do not help some, but running cas2 is not required for high memory performance. Cas to Ras delay is actually more important to performance on a A64. I've personally had good luck with all the ram I have tested with my A64 setups with the OCZ PC3500EB reining supreme. I'll list some results below (all on chaintech VNF3-250)
512MB Mushkin Level 1 PC3500:
Highest memtest86 error free overclock: 227 w 2-3-3 timings @2.9v
(Did not like running cas 2.5 on my motherboard)
2x256 Geil Ultra Platinum PC3500:
Highest memtest86 error free overclock: 240 w 2.5-3-2 timings @2.9v
(Able to run error free to 229 with 2-3-2 timings)
512MB + 256MB OCZ PC3500 EB:
Highest memtest86 error free overclock: 260 w 3-2-2 timings @ 3.05v
(hit 275 w 3-3-3 timings, but not totally stable)