There is no difference in the performance between the 2. I am told the GK's heat up more in a coweled set up because of the powdercoating. I have only 1 GK and have not used it yet. It will go into a SIG Astro Hog some day. The 91 will be fine. The 100 would work even better with the floats. It would be worth the extra bucks.

Mark Shuman