For sure, I'm that beginner you mentioned, Dan, and I'm confused.
I've read many comments on SH that the .20 FP is equal to a Fox .35, and the .25 is even more.
Mine (an ABN) turns those props as well as any of my .35s - would they also be marginal for a Banshee?
In the opinion of many, the Fox 35 is marginal for that sized plane -- which is why, starting in the late 70's, you saw 46's showing up in a lot of "35 sized" planes. However, there's a lot of holdouts, so to some extent you have to decide which camp you belong in.
Build it light, put in a 25FP, and it should be adequate, although possibly more challenging to fly. Just build it, put a 46LA in it, and once you get the engine set-up right it should be a solid, no-nonsense contest plane.
If you can stand going non-original, consider Fancherizing it. The Banshee was designed with early 70's design rules, and for an unmuffled Fox 35. That means that the tail is too small and too close to the wing compared to current contest planes, and that the nose is too long for balance with any engine with a muffler. You can fix two of the three problems by moving the wing forward a couple of inches, and then you can solve the last one with bigger tail feathers.