No, a 1GHz processor would operate at 1GHz, because it has a 7.5x multiplier and runs at 133MHz bus speed, the same bus speed as the 933 (which uses a 7x multiplier). The multiplier is locked on the CPU. The only way it wouldn't work is if the BIOS is purposely bugged not to support it. The only other issue is to make sure you get SMP capable processors, which most are.
<font color=blue>At least half of all problems are caused by an insufficient power supply!</font color=blue>