I cannot live without FI on a 3D DLP that is only 120hz, not sure what the sharp is. Motion looks horrid on 120hz projectors in 3D IMO after seeing the w7000 with FI on/off. Some people have said that "I hate the look of FI", but the motion in 3D at 120hz without FI (DLP or not) is 100x the choppiness and blur of say a JVC in regular 2D, let me put it that way. If I watch some things in 3D on the w7000 with FI disabled, it looks like an animated cartoon someone drew on flip-pages, that's how rough the motion is (slight exaggeration, but not that much). The Epson has faster panels so the Epson isn't as bad as many PJ's are without FI, but the 120hz ones without FI look very poor IMO once you see FI in 3D on a 120hz for comparison. There is a frame blur effect without it (where the image appears to be missing so many frames that they appear to be drawn onto the screen instead of natural looking).
FI is a fairly subjective feature for 2D, but in 3D on a 120hz PJ I don't think so.