Locking into one scale might give you fits if you build different scale birds. Why? Because R/C glider performance really is affected by Reynolds effect. And the full scale sailplanes have spans all over the place. So you'll wind up with some that perform well in R/C and some that are somewhat frustrating to fly.
You mention 100" span with an exclamation mark. It's actually nothing remarkable in R/C. The modern high-aspect-ratio models all wind up with long spans. The bottom line is that to get good R/C performance you need to go beyond 2m spans. The R/C performance probably doesn't matter to you very much, but it might matter if you lock into a scale that winds up giving you models that come our with spans less than 2m. You'll be winding up with models that are not much fun to fly.
The advice I'm getting to is that you don't go smaller if you can keep from it. Yeah, you might have to make some longer wings but they're going to be high aspect ratio and if made a smaller scale would have very short chords. But the advice is from a performance perspective. Go smaller and the older birds will really suffer compared to the more modern ones. The R/C performance differences will be way more than the differences seen in full scale.
If I sat down at my drafting board to do that RJ5 today, I'd want to do it to 1/7, just to get the wing almost up to 100". It would have a decent shot a being fun to fly. Of course, it's fuselage would be a handfull, but what the heck.
http://www.sailplanedirectory.com/ross.htm#RJ-5