Upload & Sell: Off
The problem may be worse on the Apple side. You not only have to upgrade the OS, you have to discard all the software that the new more-bit-depth OS can't run. Buy a lot of it again from scratch or forget about it, together with the documents you created with those programs. And you can't get a plug-in for 5D III output to run in Lightroom 3, even though they have a plug-in that lets legacy Photoshop process the files. So your choice is, you can quit using Lightroom and go back to Photoshop and Bridge, and keep using you computer as is, or revolutionize your computer, your programs, etc., and use Lightroom 4 with your 5D III. It's a pain in the butt.