What would it be?

So, I am looking for physicly the lightest laptop that can:

• be easy to carry around and light enough so that my back feels pleased that I ditched my old 15" mbp
• have stable and smooth run of AVID MC
• have stable and smooth run of ADOBE PREMIERE
• maybe even run FCP X (only as a last resort; I hate fcp X so would love not to use it anymore but some colabolators like it so... :(
• play smoothly 4K footage from cameras like sony A7sII, panasonic GH4 and such l, in finder preview/vlc player/QT player and editors mentioned above.

I need it for offline editing of documentary features, mostly via proxy 2K files but if it can edit native 4K codecs without too much hickups that is a plus. I intend to do mostly cut only editing with occasional cross dissolves, filtering, playspeed alterations etc... No major CC, sound mix etc...that will be done in pro studio enviroment!

From what I see, 13" mbp could fitt the bill. I was especialy pleased with videos that demonstrate upgrading hardware on old MBP's from 2010/2012 in order to be as efficient as the latest models. But Is there anything in PC clan that I should look out for?

I expect it to be my portable solution for on location quick video interventions and offline edit suite for another year (until 4th quarter of 2017).

Oh and of course, I expect it to be priced cery very very reasonably (bellow 1500$).

Thanks IA for everyone's input!