I have
A 40 size (Not an actual Ultra Stick - but a similar plane from a different manufacturer) with a Saito 72 on it.
A 60 size with a Saito 1.00
A 1.20 lite with a Saito 1.80

they are all great fliers and being ARF's took less than a week to build. IMHO the bigger they are the easier they are to fly but that is probably a vision thing. The bigger ones also cost more so you may be a little afraid to break them.

Look at your LHS they may have them (or similar ones) in stock at a good price. Otherwise Direct from Horizon.