I've only noticed motion artifacts when a massive image moves very fast on 1080i and 720p material. For example if they do an extreme close up of a ball carrier running through the pile. In the grand scheme of things this is minor. I think this has more to do with the source material than the projector because I notice no issues at all on 1080p Blu-ray DVDs on fast moving scenes through an OPPO BDP 93 Blu-ray player. I watched "True Grit", "Salt", and "Limitless" the past few days and didn't notice any motion artifacts whatsoever.
I only referenced the artifacts/motion issues and lack of sharpness in reference to your debate regarding screen size. My advice, go big. I had a DLP projector, the BenQ PE 7700, before this and noticed the same issues. I don't know if the newer and more expensive 1080p DLP and LCD projectors have the same issues although a few posters told me to go the DLP route if watching sports with ambient light was my main focus. Projector Replacement Debate
Their reasoning was more lumens and better with motion. I compared a JVC HD550 to a Epson 8700u and the Epson image was sharp, in fact too sharp. I do have to say this, the BenQ DLP had more "pop" or "punch" which was evident during sports even though the JVC handles ambient light a mite better. Maybe the experts on the board could explain this more thoroughly. Also football looks better on LED and plasma TVs but that's at 1/4 the size of a 119 inch screen.
That being said, I am still very happy with the JVC. I'll go home and watch some NHL hockey and let you know what I think.