I am running 24-39 in mine right now, going to try a 23-39 tomarrow(running 660'
I used to run about the same amount of HP(192HP). If memory serves my correct i got the best results from the 24-39's. What helix, springs, and weights are you running? Next time you are out doing a run, take a quick look at your speedo to see where its at(not very accurate, get a hold of a radar gun as it will be much better) and then just figure out the gearing from there(i usually run 10-15MPH more than i will reach on mine, can get away with more on 600's and stuff, but seeing as how you owned your sled for a little while you prolly know it weighs way more than a 600
One other thing to try is to make a line on your prim. with a marker and see how far your belt it going up the sheeve, a little over 3/4 way is preferable(full shift isn't very efficeint). Anyway, if you want more info just ask. Ill take a look to see what I had in there last year.