Hi Al:
I do have both the R70 and the R90. Which i fly more is hard to quantify. I love the R90 for a relaxing day of 'sport' flying. The colors and patterning present well against most skies (in Texas, ours are usually blue, but occasionally that grey haze will appear). It is probably a bit easier to maintain perspective at distance with the R90 than the R70, based on color as well as size.
You may remember that the way my R70 is set up and propped, it is a speed plane, typically 90+ mph at 3/4 throttle, and 105-110 airspeed at WOT. Running downwind with 20 knots on the surface, it covers a lot of ground quickly. Even on low rates, i have to be with it mentally all the time; she'll easily roll 540-720*/sec when wide open. The R70 snaps more quickly than the R90. The R70 also flat spins more cleanly - more horizontally - although that may be a CG issue as much as anything. The R70 enters knife edge spin well, and transitions cleanly from that to inverted flat spin. The R90 will do all that, its just a little slower, "more scale" as they say. All in all, MY R70 is a quicker, more agile aiframe than MY 90 - caps for emphasis because as you well know, the setup is at least as important as the airframe.
If you are used to the quickness and precision of an Extra / Edge / Sbach (and probably other aerobatic airframes), then the R90 will not meet that bar. On the other hand, if you want a plane that is honest, reasonably forgiving, and fun, i think the R90, like its little sister the R70, is a good buy.
Best,
Bill