1. Yep, the moment it was released.

2. Yes it did, I've had no issues with it.

3. DX11 runs perfectly fine on my PC too.

4. Yes, my game performance has increased by a few FPS. Might have been the nVidia drivers and not Windows 10 but it's the only difference I've seen.

5. So far I'm loving Windows 10 and I'd recommend the upgrade to anyone who can do it.

6. No, had no need to clean install.