Saying that size dosnt matter is like looking at it in black and white.
Yes, you can get small guys who are stronger than bigger heavier guys with the same bodyfat percentage.
Some of the strongest people i know are small athletes, and i know a lot of steroid-heads.
Yet you have to look at the simple fact, a bigger muscle is a stronger muscle.
Now that doesnt necessarily mean that somebody with a 17inch bicep will beat somebody with a 16inch, but if that persons arm grew an extra inch, yes the muscle WILL be stronger. So generally the more muscle a guy has, the stronger he is. Thats excluding fat, drugs and olympic strength training (because those guys are unreal