ok, broke a speedo cable, on an ea81 d/r 5 speed, stock tire size, in 5th gear, high range, what rpm should I be turning at 55 and 65?

I assume you dropped the 5-speed D/R in?

If so then you should be cranking about 2500 for 55, and just under 3k for 65 - 5th gear is a bit hard to approximate, the others are easier.

 

The cable is easy to get at on the tranny side (at least in EA82 cars) - fix it and forget it.

I'm going to fix it, but I need to drive the car until I get the cable

Tire size is another factor in this equation. Got a GPS unit? That's what I used to help gimme an idea of my speed.

 

Just go with the flow of traffic.

I know people that've gone 100,000 miles on a broken speedo, nah, just kiddin...

 

just run with the flow until you get it fixed