Sorry for the late reply, but one can only frequent so much forae a day...
For a cat, you aim for 30.000 rpm or more at the prop loaded, so it's a matter of doing the math with the motors you've selected.
I am currently modifying a Academy Triton with the stuff I have available and I'm using a 2300Kv 3656 motor on 4S, turning a Ø35 mm threeblade plastic prop.This gives me about 30.000 rpm under load and even though the boat is rather heavy, because there's a second 5000mAh 4S lipo on board to balance the boat, it is scaringly fast for an ABS hull that's rather narrow (offshore design).
Where you say: "I would like my cat to be 66cm and faster", should I read 66 mph?
If so, that is very fast for a 60 cm cat, I'm not saying it can't be done, but I'd rather build a bit larger hull for that kind of speed.
Which design are you going to build, if I may ask? (link?)
The 2000Kv outrunner you've selected would't be my first choice, as the rpm on 3S would be low, requiring a large prop and on 6S SAW-like high (40.000 rpm), requiring a sharpened and balanced metal prop.
The Leopard would be indeed a bi t overkill in such a small hull, but with a small prop it should work fine, as the rpm are right in the sweet spot on 3S.