A friend has a Big Stick 60 with an OS .61FX in it for a knock around plane when he isn't flying scale.
Well the FX .60 and it's clones are heavy low powered clunkers. Not much faster than my old loop scavenged K&B .61. My old HP .61 would run circles around it and many of the .75 sized engines. Now the old K&B is perfect for a .40 Big Stick. Not much heavier than a FX .46 but with more power.