so it seems that the common gear choice for these bikes are -1 in front and +2 in the back. I read somewhere that going down one in the front is the same as going up 2 in the rear... if that is indeed true, would going up 4 in the rear be the same as -1/+2?

 

It would be somewhat close; however, if you have the money, I would avoid the hassle and just do -1/+2 conversion

 

Check Out http://www.gearingcommander.com/ it will provide everything you want to know and help you figure out how far off the speedo will be once the gears are changed.