Iphone 4 ios 5 bb 04.11.08

Hi everybody, i have an iphone 4 ios 5 bb 04.11.08, right now i just make the jailbreak and it is tethered, and for so much i read the iphone doesnt have a solution for the unlock on that baseband... so, my question is... Is good or bad if i upgrade my ios to make my jailbreak be untethered and may be that way my baseband change to another that can be unlocked... and if i upgrade, wich ios do i have to install?... Thank you so much!