mxett, on a 12" tall aquarium, you will indeed want to start it fairly low. We would recommend starting at about 40%, then go from there. The Gyre XF130 should work great for a tank with those dimensions.
luvreefs23, with the aquarium being 60" long and the glass being 1/2". We would recommend the larger XF150: which worked great for the aquarium in our video that is also 60" x 24" x 24". We feel it is better to have a little bit more capacity and throttle pump back, then to have the smaller model and wishing you had a bit more.
BeanMachine, we have our fingers crossed as well.