a 25" tire diameter (for the 275/35/18) and got 203 and 186 MPH respectively. If the tires are about 1/2" taller then your numbers sound right on. I used 24.5" for stock diameter tires and wheels and get 189 MPH at 7200RPM, with a manual. It sounds like you do get it based on your calculations for the auto in 4th gear. I don't know which thread you meant where the calculations seemed off, but your projections sound on the money. Take care, Mark