Microstuttering is when 2 graphics cards get bogged down and can't communicate fast enough, so they will produce visual "hitching" because each card renders a frame, and the second card is trying to catch up with the first one (or maybe its vice versa) - either way, its the hitching that comes with running 2 gpus against their processing wall.
No way to tell if it will, but they claim their new technology will eliminate that.
I'm guessing its going to be anywhere between 10.5-11.5 inches, but we won't know until its out.
Microstuttering is the occasional lag of a single frame while the average framerates remain high (so it is annoying and noticeable, even if the average framerate is amazing). The 4870X2 should not have it, due to the changed interconnect between the dual GPUs. This is only a guess though - it could be wrong. As for length, I would guess about the same as the 3870X2.