The 9x3 should work well and I'll test them with my TP4500 + 3500 setup. I ordered the standard hub mounts and also the thin T style ones.
Full weight Mavic is 734g, 8ah of batteries 415g, plus battery mod (16ga xt30) and mounts means there's no reason to weigh more than 116x grams with 11.8 Ah.
If these propellers are drastically more efficient, it might make sense to run lighter batteries rather than the heavy 550grams of dual 4000s. It could happen that the heavy setup puts too much strain on the motors/ESCs.
It's unfortunately there there is no 8 inch version of this propeller. I'm not really wanting to cut up my body work to put these props on the rear. Are the 8x4.5 too aggressive for distance flying?