You can backfigure out what your RPMs are, from your speed, at least in sixth gear. See
this post I made a while ago.
The engine is rev limited to 8,000 RPM. The FP3 and probably the Harley Stage 1 download can lift that up to about 8500 RPM.
90 MPH in sixth gear is about 6000 RPM.
I don't know if my math is right, but it seems like 90 MPH in 5th gear would probably be about 6750 RPM, and in 4th gear it'd be about 8000 RPMs.
Someone who has a 2016+ Street, or any Street 500 or 750 with an FP3, could verify the speed at RPM calculations for us. Not a Street Rod though; it has a different size rear tire and that changes the RPM calculations. If someone wants to cruise along at 60, and report the RPMs at 60mph in 6th, 5th, and 4th, then we could update and know what the RPMs would be at 90 MPH.