Performance is often more tied to the code than to the interpreter - an O(n³) algorithm in blazing fast C won't necessarily perform any better than an O(nlogn) algorithm in Python.
An O(n³) algorithm in Python won't necessarily perform any better than an O(nlogn) algorithm in C. Ever heard of galactic algorithms?
The overhead my classmates had dealing with poorly optimised code that caused constant cache misses was far greater than the interpreter overhead in my code (though at the time I don't think I could have explained why their code was so slow compared to mine).
Oh no, this is so... good idea. Yarr! Pirate Party approves.