if i recall correctly, back when the SS was released, there was talk about the car actually being tested with the 6-spd from the 9-3 (remember, our engine and trans came from Saab), and found that without going through and completely re-engineering and calculating every ratio, the 5-spd ended up being faster and more economical. so they saved money and put the pre-existing 5-spd in, instead of spending the time and money on figuring out which ratios would be required for the 6. i can't remember where i read this at, as it was quite some time ago, and my memory could also be a bit foggy on the specifics, but i believe it was something like that.

2006 F40 (MT2)
Type: transverse front wheel drive, six
speed manual transaxle
Engine range: 3.9L
Maximum engine torque: 245 lb-ft ( 333 Nm )
Maximum gearbox torque: 295 lb-ft ( 400 Nm )
Gear ratios: MT2
First: 3.77 13.3835 final 6000 RPM 34.68 MPH
Second: 2.04 7.242 final 6000 RPM 64.08 MPH
Third: 1.32 4.686 final 6000 RPM 99.04 MPH
Fourth: 0.95 3.3725 final 6000 RPM 137.61 MPH
Fifth: 0.76 2.698 final 6000 RPM 172.02 MPH 3000 RPM 86.01mph
Sixth: 0.62 2.201 final 6000 RPM 210.86 MPH 2500 RPM 87.86 MPH 2000 RPM 70.29 MPH
Reverse: 3.54
Final Drive 3.55


2006 F35 (MU3) <<< FastFiero's choice of transmissions for the 3800SC and LS1 future installs.
Type: transverse front wheel drive, five
speed manual transaxle ( optional
with limited slip differential )
Engine range: 2.0L I-4 supercharged
Maximum engine torque: 200 lb-ft ( 271 Nm )
Maximum gearbox torque: 258 lb-ft ( 350 Nm )
Gear ratios: MU3
First: 3.38 13.6552 final 6000 RPM 33.90 MPH
Second: 1.76 7.128 final 6000 RPM 65.11 MPH
Third: 1.18 4.779 final 6000 RPM 97.11 MPH
Fourth: 0.89 3.6045 final 6000 RPM 128.76 MPH
Fifth: 0.7 2.832 final 6000 RPM 163.70 MPH 3000 RPM 81.85 MPH
Reverse: 3.17
Final Drive 4.05

bolth transmission out in 2006 1-3 gear almost identical 4th very close and then economy for the 6 speed, crap for the 5. 5th gear in the 6 speed is more economical then the 5th in the 5 speed so even if you forgot you had a 6 th gear you would still be getting better mpg's

theres nothing you can do that can't be done, all you need is CASH, and more CASH, it would not be worth the headaches!!!