It has been explained by ninja very nicely, but I'd like to add some points:
Since the 2 processors have so much of similarity, there's no point discussing raw power as they both are 19-20.
The 90k is available at ~$5 extra in most of the stores (NewEgg, Amazon), and I feel it's not a big deal.
BUT, if you're not likely to use the CPU at its most, you may save the $5, wouldn't make a difference anyways.
I go with 90K as its more value for money to me-IMHO.