Everyone missed the obvious question...
What suburb are you in and how far are you willing to travel???
If its southside then Id go with Godzilla (4wd dyno dynamics, Mark knows a thing or two about r32 GTR's, you will see when you see his workshop car)
If it were northside then Id go with Mercury (4wd dyno dynamics) or Allstar (2wd dyno logic)
My opinion, if you got a 4wd vechicle, then run it on a 4wd dyno... You want to run the car on the dyno (for tuning purposes) under the same load and usage conditions as though you were driving on the road in 4wd. Also it may also help diagnose or help point out any problems you might be having with the car.
For dyno comps its fine to pop a fuse to run level par with the GTST's in RWD, but for tuning a GTR.... Well its 4wd FTW