This is an email I got from Asus regarding differences between the revisions:
Dear valued Customer,
Thanks for Contacting ASUSTeK.
yes, the pcb 2.0 board use the crush18D chipset which can support 400Mhz processor.
but the pcb 1.4/1.6 board use the crush17D which only can support 333FSB processor.
Best Regards,
ASUS Customer Service Center Shanghai