Today I was testing a few CPU upgrades in a Digital Audio Powermac that I use for testing. I decided to try my 7448 @ 2GHz to see whether memory performance was any different to when it is installed in my Quicksilver 2002. I got the following results:

Ram Disk:> memtest disable
Allocated memory at 0x26833980 -> 0x6C4CD8BF, 1170841408 bytes
Writing and Verifying 0x00000000... Write 757 MB/sec. Verify 258 MB/sec.
Writing and Verifying 0xFFFFFFFF... Write 764 MB/sec. Verify 258 MB/sec.
Memory is ok!

A recap of my Quicksilver 2002 reults (same memory used):

Allocated memory at 0x2CB04B40 -> 0x5C9137BF, 803269760 bytes
Writing and Verifying 0x00000000...
Write 308 MB/sec. Verify 381 MB/sec.
Writing and Verifying 0xFFFFFFFF... Write 308 MB/sec. Verify 381 MB/sec.
Memory is ok!

Quite a difference...
Based on this result, maybe Digital Audio is the better choice