It's not good practice to run two processors at different speeds in SMP in any case- I've heard of times when its worked, but I don't think its guaranteed. P4-gen Xeons can match frequencies because their multis are unlocked downwardly, but I don't think P3 Xeons can do that. Conjecture, yes, but thats the basic idea behind it all- now its just a trick to find if their multipliers are indeed unlocked.