The YS are fantastic motors, however a heavy. You mentioned someone adding weight to the nose. It depends on the set up you want. I have been running OS 50's and adding tail weight with the battery and RX behind the canopy. I just put in a Irvine 53, last night, and will fly that combo today.

A buddy of mine has one with a 46 and a APC 12-4 prop. It flys the plane well, however not near as powerful as mine with a 50.

If you want to use the motors you currently own, go with the 46 and remove the baffle from the muffler. If you need more power, from there, add and ultra thrust muffler, or just buy a new motor.

The 61, I think, will not make the plane perform as you wish. I am curious of how your buddy thinks his Flip flys with all the additional nose weight. I flew one a couple of weeks ago, that felt very nose heavy, and did not like the way it flew.

You get used to whatever you are flyn.