The Rebel engine is very mildly tuned. It can be run at full load all day long without overstressing anything. I'm reminded of the specs on my '72 VW Beetle as recorded in the owner's manual..... Top speed 82 MPH... Maximum cruising speed 82 MPH.. The Rebel is about the same.
However, since I'm used to big fast motorcycles, I will say that the Rebel is a bit stressful on the rider to cruise fast on the highway. Its all strung out at 70-75 and has no reserve at all for passing or a headwind. Being small and light weight has a certain charm, but Rebels are definitely happier on back roads cruising at 50-60 MPH than pushing for top speed on the superslab.
2004 Rebel 250, 2003 BMW K1200GT (roadburner), 2004 BMW R1200GS(all purpose),
1973 Norton Interstate (in a box in the basement)
1968 Triumph Bonneville