Re: What's the most tread for the 20" I can buy?
I just put the Nitto Terra Grapplers on in the stock P265/50/20 size. Other than the price (Owwie!) I have been deliriously happy with them so far. Not too bad on the noise at freeway speed, and terrific in the snow and slush.
Much like yourself, I always felt the Forteras were a little skittish in the snow, and down right miserable in sand or soft dirt. The AT Nittos really seem to have helped.