This is from the Dec 2004 issue of Car and Driver:
It's for a 2005 GT with the 5 speed manual, the 2006 GT should be identical.
1st Gear
Ratio: 3.34
Mph/1,000 RPM: 6.6
2nd Gear
Ratio: 2.00
Mph/1,000 RPM: 11.0
3rd Gear
Ratio: 1.32
Mph/1,000 RPM: 16.7
4th Gear
Ratio: 1.00
Mph/1,000 RPM: 22.0
5th Gear
Ratio: 0.67
Mph/1,000 RPM: 32.8