No, the 2012 Unibody MBPs do not have the infamous "Radeongate" GPU issue, that is on the 2011 15/17" MBPs.
Here's the question -
do you want upgradability? If so, get the unibody with only 1 GB of VRAM (you HAVE to get the 2.6 GHz Core i7 configuration to get 1 GB - otherwise it's 512 MB of VRAM in lower configs). If not, get the 2013 15".
I know for a
fact that the 2012 MBP will NOT handle 4K at the full resolution (I've tried 4K 60 fps on a 2012 27" iMac with the max configuration - 32 GB of RAM, 3.5 GHz i7, and the GTX 680MX with 2 GB of VRAM, and that BARELY worked) - so I'd imagine the unibody would definitely not do it at full-res.
Be ready to:
- Turn down the resolution to half, or even quarter if you add multiple streams, effects, etc.
- Do some background rendering when you edit (especially if you use Davinci Resolve like I do)
I'm going to get an older iMac just to have a desktop laying around, so I might as well suggest it to you - You might also consider getting an iMac (27") if you want a little more power. eBay has 2012 27" iMacs for around $300-350 that look pretty decent...
Hope this helps!