sorry,these posts have me smiling.
Once you guys get that motion blur keyed, you'll find that almost overnight, you are better compositors! This is one of those things you can't explain properly in forums, people just have to get in there and do it to see how big of a problem it is. You know what I mean? Like, people are always posting things like "I hate Keylight, it always leaves dark lines around my keys" or "How do I get rid of all that noise in the blurry parts of my key?". People seem to think that stuff should just magically key away, and it doesn't. This is why keys sometimes take WEEKS to do! This is the kind of thing people don't understand until they have to deal with it themselves. And you guys are! Isn't it great!!
There is one solution - garbage rotos. I know you hate to hear it. EVERYONE does. Who likes roto? NO ONE. But it exists for a reason. More often than not, it's the only way.
Do garbage rotos around EVERY individual section. Like, if the arm is blurry, garbage roto the edge. Like this:
Then, separate out those parts into their own layers and KEY THEM ALL SEPARATELY. Use feathering and expansion settings on the garbage masks to blend them all together so there's no gaps.
Also, don't be afraid to use the individual color channels! Usually one of the channels is very contrasty, and you can just straight up use that as an instant matte, no keying involved, you just may have to tweak the levels on it once you've converted it to a matte. The channels will ALWAYS and DEFINITELY give you a smoother gradient than you're going to get with any keyer.
Also keep in mind that how that blur looks is VERY dependant on the background you're putting behind it. For example, if you put a really dark background, you will have to do a COMPLETELY different key then if you put it over a really light background.
A few times, in extreme cases where nothing would work, I would roto OUT all of the blur, then, using a very precise, feathered roto of the blurry areas, I would use a solid to "cheat" back in the blurry parts. Basically recreating them with a solid and roto. Which sucks. But, hey, that compositing!!