Crossing RPM should be just about the time that your "average" HP starts to fall off and not based on the peak. I would be leary of using desktop dyno to determine a rear gear, but I am pretty sure that you are heading in the right direction.

I can give a real life example. All the following info is found on my custom cam card: Basic cam info: .598/.587 lift, 234/248 duration. Peak HP was estimated at 5800rpm. Shift point is 6400rpm and the RPM to cross the traps is 6700rpm.

For this example, a 4.56 would be just about ideal using my 26" tall tire.

For me, reality has to set in too. I am not really interested in running 4.56's on the street and thus I compromise by using the 4.11's and cross at 6200rpm.

What is the height of your rear tires? My uneducated guess would be that either a 4.56 or a 4.88 would maximize your combo better (if your tires were also 26" tall.) Since you are pushing 500lbs more than me, I would lean toward the latter in this example.

Underdrive pulleys will certainly help. I use a 4" alternator pulley and the stock type water pump stuff--but I only max it out to 6700rpm.

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Dennis
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65' STANG (3330 lbs), 393W NA, Toploader 4 Spd, 4:11, AFR 205's, Vic Jr. Intake, CI Custom SFT, 750dp, 11.0 CR

11.25@122.19mph