4.10 and speedometer worries

Hi everybody!

First time poster, long time reader.

I know that this has been covered before, but I'm looking for some up to date info and most people on here seem real nice when it comes to helping people out with problems, so here's mine:

I'm looking to upgrade my gears to 4.10's (FRPP) due to the raves on these forums. My only concern is that the speedometer gets thrown out of whack. I've read about the harness you can purchase and the plastic gear (which I'm not interested in). My main question is "How bad does the gear swap mess up the speedo and how easy is it to install the harness for someone with average wiring skills?" Does everybody that does the gear swap adjust the speedometer?

Any other information you can provide will be used as proof that you are gods among newbs.

Thanks alot guys ( )that helps me out with my options. That speed cal by Brothers perfomance would probably be my best choice. I'll probably buy the gears first and the cal later and have them installed at the same time. Sure gonna be anxious to get the gear installed while waiting for the speed cal.