Since you want proportional fonts, you'd have to be willing to leave the terminal already. If so, I'm aware of three options:
1. the classic, xman: fugly
2. the builtin, "man -H": it works sometimes. On my own system, the it's so unreliable that I'd call it alpha-stage software
3. and Konqueror. Works perfectly every time, but you'd have to install KDE components.