Currently working on a biggish project in the studio running the 5D3 tethered, OSX 10.7.5 with EOS Utility 12.2.0.
And it's 100% stable! Since I got the 5D3, tethered shooting was a hit and miss affair, constant freezing, crashing and embellished with a boatload of four letter words. But at least I have been able to work, unlike those who are running OSX 10.8.x. It's just plain good luck that I didn't buy the 10.8.0 upgrade.
Anyway, we're all happy now. Back to work!