I had them top out much faster than that, the needle stops responding (I think, was quite a few years ago now) but the mileage still went up. Each speedo was slightly different though. Hmmm, now I think about it perhaps the sender is the limiting factor as I was using a function generator so didn't need the sender.
Anyway, so long as it works then who cares how it looks
You've also got a far clearer bench than I have ever had.