Something similar was discussed here: http://www.luminous-landscape.com/forum/index.php?topic=44622.0
I must ad that I found the vintage manual primes much more suitable for video and indeed that can deserve top performances on a ridiculous price in e-bay.
I precisely kept the Pentax mount for this because there is no other dslr system that has such a full grade of integration with their mount and such a big choice in the vintage market.
So I can use vintage manual primes with full functions, no need adapter, nothing. It bloody works, focus led viewfinder is trustable even in low light and for video, it bloody works very well.
A very interesting alternative to the Canons.
As an example, I always use the Canon when it comes to the pro tasks, I have to. But I find myself never choosing the Canon when I'm doing my own stuff and always choose the Pentax. Why? because it works much better with the lenses. It has some downsides (motion jpegs) but in real work they are more suitables. It's not very well known, people always think Canon, but I've gave my Pentax to some videographers that where working with the Canon and they didn't want to give it back to me...true!