Its been my experience that the extra weight of the AX and Pro engines helps the cg as most planes including an LT40 trainer I had need extra nose weight to balance anyway. Its better to have extra weight as a stronger, better engine rather than lead slugs that do nothing. Re: >"I have no interest in non-OS engines"< this may be a valid view for 46 size engines but by this I refer to the FX and AX series. I think they are still the best in that size range. The LA series are weak and have limited uses. For larger sizes though I have an OS 61 engine although reliable, the power output isn't all that impressive, especially for the price. I have tried 3 other brands in this size range and for me the best engine is the Tower Hobbies 75. Just my 2 cents.