stock tach
 

i have an 89 lx, and i was wondering how far the tach is off when i rev up to about 5000 rpm, and if it is off about how much and in which direction

When I went to the dyno my tack was off by about 800 RPMs. When my tack read 6300 RPMs I was actually at 5,500 RPMs.

Its not so much that they are off xxx-rpm... Its more like that they arent as responsive as say my Autometer.
THey move radically different, imagine telling two drivers to rev their motors... "ok, now..." not even close!
I was tired of watching the two move so differently, that I disconnected the stock one cause it was anoying!

http://www.dariusrudis.com/stuff/2000_890.jpg

Furthermore, at idle, my tach was off by about 200 RPMs.