If it puts out 100 watts on a lesser gain, it will put 100 watts out on a higher gain.
The only thing maxing out the gain on your amps means is that you can't turn your HU up as loud without it clipping. It's actually practical to set all your amps equally if you don't know your HUs voltage. All you sacrifice is a level of control over volume, your speakers will clip at like.. 15/50 instead of 36/50, so you now only have 15 different levels of volume.
My friend has the exact same Dual amp. Bridged it puts out 300 watts. He also has 2 Dual 12's. It's not a bad setup suprisingly. It took me a while to get the volume, crossover, and bass boost adjusted to where it sounds good but when I did, it sounded pretty **** good *for a 200 dollar package deal*.