I run 28x10.5 PBR since I have my car, never ran a bias ply. I usually have a 1.42-1.43 60' running 18psi of air. I have only spun the tires if something was really wrong with the track and that has only been about 3 times. I used to run as springs but now have the full calvert setup. My only complaint is that they don't make them in a 29x12.5
I currently run a 12" wide slick and I think the widest radial slick is 10.5 or 11. I'd be nervous about going down in width. Also I don't know if they will go on a 12" wide wheel.