I also have a ZRX1200 which is a torque monster. I expected the z900 to feel gutless next to it but that is not the case. The ZRX has torque everywhere, the z900 has torque almost everywhere by comparison. When the testers consider the z900 a torquey bike you can believe them.
I had mentioned that I went UP one tooth on my Versys 650 to calm it down on the highway, which it did plus it lengthened the amount of time before I had to shift from first to second. Yet even though the V was only 60 HP with something like 45 ft/lb of torque the difference between the fore and after, powerwise, wasn't noticeable at all.
So do the front first, if you need more then do the rear but I don't think you'll need to. And don't worry about the power, she's got it.