I think part of the answer depends on what kind of 20 you are looking at.

Using the 46 - 50 size range as an example of what I mean, there is a BIG difference between the power of and OS 46 LA and an OS 46 FX. Even more difference when you get into somthing like the Irvine 53, OS 50sx, and higher engines like the JETT engines.

For something like an OS 25 LA you may want to look at the Hangar 9 power 25 BL, it seems to similar.

Based on your original post, you may want to consider the power 15 also.