For 4.4 stable, as you can expect, the answer is probably truthfullly "when it is ready". I know it's very close but could still be a couple of months possibly. I'm guessing even Marc doesn't know 100%.
While you can use 4.3 in production (we do) I would strongly caution that this is really a nightly build train. As new features are introduced and things are "fixed" from a programming or architecture perspective, it can and does break certain features that you may have configured in a certain way. I would urge you to test everything that is important to you before rolling out updates on the 4.3 branch as things will "break" quite commonly simply due to behavior changes.
On the master branch, not much is done to ensure that you won't experience any regressions between versions because new features are added and parts of the software are rewritten regularly. So yeah, you can run it, but be very careful and do your testing between upgrades if you want to run master!
