I did some actual racing at an all Ford event last Sunday and ran consistent 13.1s all day long.
60ft was 2.125
I think I'd probably be safe moving to a 3.0 pulley on my Saleen at this altitude. I just don't know which size belt I would need to go with the 3.0 pulley.
Another guy with a 2006 Mustang and a Whipple was running mid and low 12 ETs with a 2.90 Whipple pulley. He was still using the 6 rib and had a Reichard tensioner. But his supporting mods were basically just like mine. Although he did have the advantage of using some Toyo drag radials too. Plus he has 3.73 gears and mine are the 3.31 gears.