out of those 3 I would not buy the OS, after owning an OS 61Fx the OS wouldn't even be a thought for me,
but lets look at the Saito 180, when I had a Magnum 180 4St (thank god it's gone now) I read a lot on the Saito 180's performance, the Saito should turn an APC 17X8 at 8,800 to 9,000, and a few reported 9,100,, all on 10% to 20% Nitro, but the thing is that I learned "after" buying that Magnum is you I could have bought a pre-owned Saito 180 that was never started for the same price or even less than what I paid for that Magnum.. if you want a smooth plane buy the Saito.
this RCU thread tells the story that the Moki 180 is one big flying monster on 0% to 5% Nitro, so if you want to go fast it's the engine you want, but for sure, unlike the Saito the Moki will be eating a lot of 0%
http://www.rcuniverse.com/forum/tach...rformance.html
Jim