Speedo Gear Question, plus needle bounce

[davepl]

I made a few minor changes to my speedo calibration:

- New speedo warning head from unknown ratio truck
- New trans with overdrive and unknown expected rear end ratio
- Different rear end ratio
- Taller tires

So, as you can see, all bets were off. But driving by a speed sign I magically found it said 38 when I was at 36. I figure that's close enough, but would I get much closer if I did the math on the error and changed a gear?

Also, I have a tiny bit of needle bounce, like in a 2-3mph window. Anything I can do about that doesn't require rebuilding the speedo? Cable is silent and new.