To be honest that doesn't prove a lot.

I first flew my LT-40 with an Irvine 39 then switched to an OS46FX. These two engines might show a big difference in some airframes, but in the LT-40 any difference was hardly noticable. If anything, the FX was worse as the plane dropped its nose more when power was removed. And yes, I did make sure to compensate for the extra weight by moving the battery back.

However, installing the FS70 did make a big difference, but I wouldn't recommend this combo for a beginner as the extra weight affects the handling and there's virtually no prop clearance...