Dear Motherboard Gurus.... tell me if ...

.... it would do any harm to plug in a CPU of a higher FSB rating than
the MOBO is designed for ?
My mobo has a fsb rating of 400MHz but my P4s rating is 800Mhz.
I personally feel it woud do no (physical) harm except, perhaps,
to 'pull down' the P4's capability and cause it to be under-utilised?
Please correct me if I'm wrong
thnx