If you look in the instrument portion of the shop manual, there is a gauge tester that is a simple resistor box with three settings low, mid, high which correspond to the gauge positions. There is also a way to test all three gauges using a fuel tank sender which would imply that the resistance values are very close if not the same.

One of the things I have observed over the years with my Fords is on a long highway run they will slowly read higher, particularly the oil pressure as that is the most noticeable.

On my Shelby, I had a mechanical gauge in addition to the electric one. The engine held 65psi on the highway which was 2/3 of the way on the dash gauge. On a run to VIR, about the point you needed to stop for a rest break, it would be closer to 3/4 scale, but the mechanical one still showed 65psi.