From the Preface to Dr. Conway's book, Object Oriented Perl:
in reply to object oriented performance
A single method call is about 30 percent slower than a regular call to the same subroutine (depending on your hardware, your operating system, the phase of the moon, etc.) But though they're individually much slower, method calls are more powerful than regular subrotine calls, due to a feature known as polymorphism (see chapters 1 and 7). In a larger system, that redresses the speed imbalance in a little [sic], but in general, it's fair to say that an object-oriented implementation of a system in Perl will almost never be faster than the equivalent non-object-oriented implementation, and will usually be somewhere between 20 to 50 percent slower."
But, he goes on to say, there are many compensating benefits, and he then lists them.
I just got the book today-- it looks terrific!
Published by Manning Publications Co. (http://www.manning.com), but I got mine through bookpool.com (click) for only $28.50 -- 34% off the cover price. I love that outfit.