I run mine at 45 also, with occasional quick jaunts up to 55.
They say that the "red line" on a 216 is somewhere in the neighborhood of 3000-3500 RPM. Just so long as you don't rev the engine higher than that, you should be fine.
Approximate RPM Breakdown in High Gear:
25 MPH ≈ 1300 RPM
30 MPH ≈ 1600 RPM
35 MPH ≈ 1900 RPM
40 MPH ≈ 2100 RPM
45 MPH ≈ 2400 RPM
50 MPH ≈ 2700 RPM
55 MPH ≈ 2900 RPM
Your numbers may vary based on gear ratio (should be around 4.55:1), transmission ratio (should be 1:1) and tire diameter.
