If you're flashing a ROM than you're not getting the official OTA for Jellybean when it happens. Also you're assuming official Jellybean will be rootable from day 1 which more than likely won't be the case. If you want JB now than flash cyanogenmod10 and enjoy it, otherwise sit back and wait for the OTA and root if you want to use root apps/freeze bloat. If you take an OTA while stock rooted the worst case scenario is that you'll lose root access. Not a life ruiner. Also don't expect the official JB update to be much different than what you have now. It's gonna have Touchwiz crammed into it ya know.
Sent From My Rooted/Modded SGSIII - If I've helped you please click 'Thanks'!