The 1985+ R65 bike engines were retuned for torque peak lower in the RPM band and fitted with the same 3.36 final drives that the torquier R80 engine had, but apparently the R65 engine could pull it without too much difficulty. If you go to a "taller" final drive like a 3.0 or 2.92 from an R100, I think that you'll have to do alot more frequent shifting, and revving the motor alot more to achieve decent acceleration & overtaking, plus being more likely to lug the 248 engine, which really shouldn't be lugged (the Type 247 engine in the R75/R80/R100 bikes shouldn't be lugged either, but they are still tuned for lower torque peaks than the rev-happy 248 engine).
There was a time when I pursued triple digit speeds on public highways on motorcycles - fortunately I think that I'm mostly past that now and am quite happy keeping my motorcycles below the ton (though sometimes not too far below it). Speeding tickets round these parts for doing 100+ MPH will get you put in jail, automatically, anyhow.
One advantage of the 3.36 final drive on your R65 might be to nudge the typical "buzzy" point that usually occurs just above 4500 RPM on my bike to be around 70 MPH - thus you could cruise at the typical speed limit in a smoother RPM band for a few more MPH. I generally just either ride the thing at 62 MPH, or else at 72 MPH, and avoid the buzzy area altogether with my stock 3.56:1.
