I don't think that information is true. When overclocking my WarpEngine I change the crystal towards the edge connector (on mine its next to label U9) I can run a 45Mhz crystal reliably and can run a 48Mhz one for a short while.
This does not alter the SCSI transfer.
According to
http://members.iinet.net.au/~davem2/overclock/warp.html
The corner Crystal is devided by two to drive the SCSI and motherboard at 25Mhz.
I have not tried playing around with that crystal and just leave it at 50Mhz.