OS "ABN" liner/piston assemblies are made for easy handling and short run-in time. Hard use in competition could lead to loss of top-power but they would still be ok for Sport flying.

I've converted several OS Max 46FX to the ringed piston/liner from the helicopter FX46 engine. They run great and 16-17000 rpm is exactly the optimum for these engines.

The steel liner with ringed piston should last very long with consistent power output.

To buy the spare parts for the conversion may be a little expensive. OS part numbers are listed here: http://www.osengines.com/parts/xr15470.html

I got the parts from cheap offers I found on eBay because the 46-size is not very common anymore in heli-flying.
You can also drop one of the 46FX-H Heli engines in as-is and fly it as an airplane engine.

What props are you using according to you competition rules?

PS: 10 years ago I used Super Tigre G40 ringed for Q500 Sport (tuned muffler and 10x6 APC) and a G500 ABC for open Q500 Pylon racing (ST G500 tuned muffler 8,75x7-8 APC) and they both ran great. Fuel was FAI 20/80 Castor mix. Especially the G40 had great power output compared to the OS and other engines and I still use it today with smaller props and more nitro just for fun. The engine is still running strong and really likes the rpm range betweet 15k and 17k.
If you can get some Super Tigre 45 ABC you might have a competitive and long lasting engine.My experience applies to the "Made in Italy" versions.