The YS 1.10 is much stronger than the OS 1.20. The OS.91 pumped isn't even in the contest and their trouble record is far worse than the YS 1.10. High performance flying is a costly adventure, unfortunately.

A Saito 1.25 would be a better choice than any OS four-stroke. It is very light, relatively speaking. Combine this with the Cline or Iron Bay regulator that you will need and you could have paid for a YS 1.10.

If you want a powerful set up for cheap, get a Super Tigre G90, a Magnum 90-108 or Perry carb and a Cline or Iron Bay regulator. Lots of power and reliability (after tossing the ST glow plug), will last a long, long time and you'll have no valves to adjust. Another plus is that it will run happily on 5% nitro fuel. Just my $.02.