Ok well the T56 transmission is a Tremec transmission used by General Motors. The Getrag 6 speed manual is not a T56. The Getrag 6 speed is used by Toyota, Mitsubishi, Dodge, Ford, and it is also used by Pontiac (GM) and many others. But each company uses a different version of the manual. So it depends on exactly which Getrag 6-speed variant it is.
The VZ V6's use a D173 Aisin 6-speed Manual Transmission. This transmission is built in Japan and the SV6 was the first car in the world to use it. Ratio's are as following:
First: 4.48
Second: 2.58
Third: 1.63
Fourth: 1.19
Fifth: 1.00
Sixth: 0.75
The VZ V8's use the original Tremec T56 6-speed Manual Transmission which has been in use since the VT. Gear ratio's are:
First: 2.66
Second: 1.78
Third: 1.30
Fourth: 1.00
Fifth: 0.74
Sixth: 0.50
The VZ Monaro however uses an M12 version of the Tremec T56 6-speed Manual Transmission which generally in the GM empire is not used in applications of much over 400hp, but it can handle more. Gear ratio's are as following:
First: 2.97
Second: 2.07
Third: 1.43
Fourth: 1.00
Fifth: 0.84
Sixth: 0.57
The M12 T56 would be the strongest of the transmissions that Holden use.