Maybe it's a difference in perception but both my 300SDs were very relaxed and comfortable at 80 including runs from SJ to SF on 280. Mind you it sounds like you're in a B-17 but there's no reason to think engineers came up with the 85mph speedo. I don't recall how difficult it was to run up 92 but even the SDL needed to have its momentum up by Anza Blvd to not embarass itself. Speed limit is 55 there but you either go 70 in the left lane with a Range Rover riding your tail or 40 behind a semi in the right lane :/

If you want to test your SD, I know a guy who uses a measured stretch of Calaveras Blvd east of 680 as a baseline. He ended up with my 83 SD which just about edged his Silver State Classic 84 SD (SSC midpoint speed = 115mph!) on the same stretch. Not a race, different dates, different times of year, maybe the same stopwatch

Maybe you're sitting too far back and it's your ankle that has to work a little bit

Sixto
93 300SD