IMHO the plastic/cf mix Gemfan props are a waste of time and money. I'll send you a bunch if you want 'em.
You're on the right path with careful balancing. But unbalanced hub is not a balanced prop. The prop should stay in any position you stop it in when on the balancer. And yes those hubs are horrible... often you can see how far off-center the holes are.
Lastly, I had to throw half of those props away because they would loose tracking when under any load. Bad for any flying vehicle, but truly horrible on MRs.
The full-carbon Gemfans are quite nice OTOH. VERY stiff. Better and more consistent than the wooden JXFs I've tried (the JXFs had only one decent prop out of every 3 in my batch of 18 in 3 different sizes). The carbon ones have almost no "transition point" vibrations at all (don't know if that's the right term for it... the point where the prop really starts biting and the blades tips want to lift up, very obvious on plastic props and even the JXF woodies).
For plastic props, since Graupner is out for now, I'd stick with APC, especially the E types, as they're stiffer.
Props are vital. My Y6 can go from "great" to "bleh" just by changing out the make/model of the props, even when they're all perfectly balanced. Very obvious in the graphs too.
-Max