Foreign key constraints with MySQL/InnoDB I am try to do some performance testing with varchar foreign keys vs int foreign keys and was wondering how foreign key constraints effect performance of MySQL.  

I assume that they effect inserted/updates to a degree however I am not to worried about that in my testing.  I was wondering if they effect SELECT statements and if they effect data/index size?
"integers are cheaper to compare than characters, because character sets and collations (sorting rules) make character comparisons complicated. Integers are very good when using as an index column." - HottestGuide