I can't say I'd use some review benchmark as a valid reason for getting rid of a perfectly good functional device. In terms of real world usage you really aren't going to notice the performance decrease due to the filesystem being on flash memory, sure a couple of programs may take a few seconds longer to start up but surely it's worth it for security of data.
I'm sure I've seen a ramdrive type program for pocket PCs, surely you can use that instead of selling a perfectly good X51...
Ramdrive for WM5 (not tested on X51 tho)
http://buzzdev.net/content/view/22/45/
This seems to be specifically for the HTC Himalaya, don't know if it works on our devices....