Personal observation...1-3 lbs is pretty normal, with 4 or better HUGE. I have heard, but not seen myself, of males in the 7-8 range (and why can I never find of these guys during a tournament?).
You will usually see the largest females that you see on beds with larger males. Not always, but usually.
Worked with a professor on some biomonitoring experiments using largemouth one summer. I caught around 50 bass (in Louisiana waterways that would likely be almost pure northern strain) and we determined sex. Not a one over 2 lbs was a male. I caught fish from 1-5 lbs.
