Sounds about like mine.
2001 TW, 14/47 gearing with o-ring chain, TW203/204 road tires. 160 pounds no hugging, no wind - 75 degrees - 70 mph maximum. The speed gauge is 100% accurate so this is a true 70 mph. I hit 75 down a steep hill, but I'm almost certain this would never happen on any flat land. A long enough steep enough hill would definitely let the bike hit red line in 5th, which should be 79-80 mph.
With the right amount of wind and/or hills, the bike may struggle to hit 55-60, which really sucks and kills the bikes highway ability for real-world riding in any condition - that'sn why I say screw the highway and use the TW as a backroad blaster!