As far as sharpness, the kit lens in video will be just as good; read the stuff Barry Green has written about this. However, if you need a faster lens, that's a different story.
I agree, but there isn't glass that is soft enough out there, and like most I am trying to build a kit of superb glass to use with any camera. Red will have an electronic canon mount and all of those lenses that will cover 6k will also do a very good job at resolving enough detail for 6k. If the 7D has issues then the solution isn't to buy old glass (unless you can spare the cash) but to try to rush your investment in a MB that will work with whatever camera you may end up using in the future and get a softening filter or two. It is probably going to be a lot more money but it would be best if you can work it out. But right and buy once. In the end the only one that knows what's best for you is yourself.