marciorr, let us know how 2 sticks works out. I had a buddy who also had problems running 4 sticks with any kind of overclock or timing tweaks.
Everything I have seen points to 4 sticks being problematic at tight timings of any kind, whether it be command rate or CAS lantency, etc. I forget if this is the fault of the Nforce4 chipset, or the on-die memory controller on the A64.
Either way, it does make working with 4 sticks not very fun unless you dont care about timings at all (as in, they would prolly run stable at 2T, CAS 2.5 or 3, if you stick around the 200mhz mark.)