That is awesome 866. I have seen Steve drive plenty. He is good.
The last few mph come with experience. A properly setup 18 with a 6.2 will do right at 70. A first timer won't see much over 65. The 71-72 mph stuff with that setp is the perfect day (light load, chop, warm water, cool air, downhill with the windshield wipers on etc. With decent skill you can hit 68-70.
Up that ante and all these variances are bigger.
2001 35 Fountain Lightning w500 EFI's
1973 X-18 - Merc 383 Magnum
1974 Chris Craft Roamer with 1271 TI's