A few personal opinions which may or may not be correct:

I do not have the Enya-IV .15, but my Enya-III .15 runs fine on 15% nitro, 22% castor oil, and an 8x4 prop. I think a 8x4 prop for a sport model will out-pull a 7x6. Were it a sleek, streamlined model I would go with the 7x6.

I think the Max .25RC in question is the older iron/steel with drop-in liner that replaced the steel fin Max engines. OS has always enjoyed a good rep to most. Same fuel as Enya.

I do not have an LA .25 but the FP .25 is a good engine. I think the porting was changed on the LA. My understanding is that they eliminated the boost port. This SHOULD give the similar power until you get to the higher RPM range, then the FP should have the edge.

As stated, these are only opinions, individual results may vary.

George