H1b Nearing 6 years, approved I-140 - can I change jobs now?

[arvindrang]

Hi,

Few facts:
Company A:
I got my H1B in Dec 2009
Approved labor and Approved I-140 - Priority date - Jan 2011

Company B:
Joined Company B in Feb 2012
Applied for perm and got labor cleared - May 2014

H1B expiring Jan 2015.

I am eligible for 3 year H1B extension which my company B plans to do soon.

My question is:
1. I know I can get 3 year H1B extension if I do not switch jobs (even after 6 yr H1B visa). Can I join Company C now and get 3 year H1b extension ?
2. In my new company C, will I be able to use the same priority date (yes the process will have to be started again).
3. Is there any restriction of what needs to be done before Jan 2015 (H1B expires?) like labor needs to be cleared etc?

Please let me know if it is safe to switch jobs at this point keeping my priority dates?

Thanks.