RE: YS 63FZ-S or saito 72
Saito 82 is more of a direct comparison to the YS 63, that is they are approximate in weight and cost, with the hair splitting in favor of the Saito most times.
If you tend to fly your planes WOT and speed is the objective then the YS 63 probably makes more sense. If you want a little more modulation (torque) in the lower rpms then the Saito would probably do better. In other words, the power curve of the YS is steeper like a 4 cylinder turbo charged engine, where the power curve of the Saito is going to be broader, like a V8.
Truly, you are splitting hairs when comparing these two engines (YS 63 vs. Saito 82). Get the one that is cheapest!
If you insist on a comparison to the .72 GK, the YS is going to outperform the Saito .72, like Richard said. The GK will either look a lot better or a lot worse depending on aesthetics. Personally, I don't much care what the engine 'looks' like.