It's very, very close to your limits as I understand them to be. If you end up trapping 125, that'll be 6750-ish with the 4.10's if you're precisely at 6000 and 122.3 with 3.73's now. If your tach lags a little and you were actually at 6050 you might just hit a 6800 limiter. Kind of what I'm saying is that the uncertainties could easily be half as large as the change that you're hoping to achieve, and that makes predictions difficult.

BTW, I couldn't find that size tire.


Norm

Stage4 - 4th gear is direct, or 1.00 to 1.

When I'm being fussy, I work from the revs per mile provided by the mfr. That's about the best that you can do short of doing your own carefully controlled and instrumented testing.

For less fussy stuff, tire revs per mile can be taken as
20900/[TireDiameter, inches]

You'll probably see something like
20168/[TireDiameter, inches]
in any number of online calculators that provide the equations for reference, and that's the formula that all of the ones I've checked are based on. Every single one of them gives 27.25" and 740 revs per mile for the 235/50-18 that's the optional GT tire (and does ~770 revs per mile)

However, that formula with the 20168 factor overestimates the road speed for most road tires by 3 to 3.5% because it does not correct for tire tread compression where it contacts the ground. It is good enough for most ordinary folks and their usual interest of reasonably close speedometer accuracy at 60 to 70 mph, but not in cases like this one when you're squeezed between being able to use the best part of your power curve without hitting your rev-limiter when peak power occurs close to your rev limit.

Using Tire Diameter = 2 times the loaded radius is no better, as that underestimates road speed by a similar amount.

None of the above methods work for Top Fuel or similar slicks that grow appreciably due to the combination of extreme centifugal force at high tire revs, soft carcass construction, and presumably low inflation pressures.

Norm