Hi.
I'm using an old MB called Asus P4T533-C with RDRAM (PC800).
As I'd like to upgrade the CPU from a P4 1.8 GHz (400Mhz FSB) to a P4 2.8 533Mhz FSB,  and would like to keep using my old PC800 memories, I have ran into a compatibility question I'd like answered before I go ahead and buy a CPU.  
 
From what I've read so far it seems PC800 RDRAM wont work with a CPU using 533Mhz FSB. Or is that only certain types, like the NEC ones?
 
Since the P4T533-C MB has the option to run at 400Mhz FSB mode (which I'm currently using), can I run a P4 533Mhz FSB CPU (Northwood core) in the 400Mhz FSB mode?  
If so, what kind of effect would it have? The reason to do this would obviously be to be able to use my PC800 memories, but if it means the CPU wont run at 2.8 Ghz then there's little reason.
 
I know this is an old MB, but I'm hoping there's still someone who knows these things. Thanks .