Bogging in the midrange usually means that the idle mixture is too rich. You may need to lean it a bit. You may also have the high-speed needle improperly-set. Get the engine set first, and ignore temperatures. How does the engine run at full throttle? How does it idle? How does it transition? If the engine runs well throughout the throttle range, then you have it properly-set, regardless of any temp reading. If you set your engine based upon temps, then you'll never get it set correctly. If you are using a low-oil racing fuel, then you can count on needing to replace the piston/liner assembly after a few races or after a few gallons. Low-oil fuel contributes to good racing and short engine life.

The high-speed needle should be set just rich of peak RPM. When you accelerate up to full throttle the engine should come up and then hold. It should not come up and then drop in RPM. If it comes up and drops, the high-speed needle is too lean. The idle mixture should be set so that you get a good idle with good throttle-up. Adjust it as necessary to get a clean throttle transition.

Higher-oil fuels will give you longer engine life, but will also take a bit longer to clear when you punch the throttle. Top-end will be about the same. If you're not racing, then a regular airplane-type fuel would be the best all-around solution. You can get those fuels with nitro up to 30%...whatever you want, really.