engine help
Bushing .40's like the TT .42 and the OS 40 FP and LA have similar power to most hot (Bearing) .25's.
In the QHOR/SPA3D style planes, people were using .40's in the 25 size all the time, and .60/.75's in the .46 sizes with little trouble at all.
What type of SPAD were you thinking of overpowering?