Cool find. I've got lot's of multi-tools but this would be nice as an always-on-me backup.
Personally, I'd either go on Amazon right this second and 2-day a video monopod (it's possible that you can use the head from your tripod and just purchase the leg of the monopod), or rent some lenses with IS.
Few things: I've never tried editing 4K h.264 on it, but I have the same MBP for remotes and it edits 4K ProRes just fine (I use FCPX). Try transcoding it. I'd also try a better SSD if that doesn't help. However, you can't expect to run at full quality AND apply effects with that computer.
Like Guy said, the housing is the only thing that makes these "cine lenses" so you can look at the optical quality reviews of the stills lenses. Rokinon and Samyang are the same company so check out these DXO ratings: http://www.dxomark.com/best-samyang-lenses . For some reason they don't have results for the 50mm, though.
One thing I'd like to add which hasn't been mentioned: I think goals need to be taken into account in order to weigh in on "short vs feature." Is the project to:
-Augment your reel to get hired on other projects?
-Enter into festivals?
-Shop around for funding?
For any of these, really, I'd actually say pulling a pivotal scene (or 2) from a feature screenplay you want to make and filming that as a proof-of-concept is the best option. It adds to your reel, of course, and ANYONE can make a few scenes work better than trying to pull off an entire feature with no budget. Then go to festivals with your impressive scene(s) and network your ass off to get producers on-board for a feature with a real budget and kick some ass.
I've had several producers tell me to go this route for my next project.
NOBODY has told me to make a zero-budget feature, on the other hand.
Personally, I use iShowU from shinywhitebox and it does the job for me. I have no experience with other software.