Mega Man is +MFTL not because he was standing on Rush, but because he was piloting Rush during that space sequence. So him dodging the Wily Star's lasers were solely based on his quick reactions and impulses which is 250x faster than light. That goes for the asteroid belt too, but it's 25x. Other examples of reaction speed are when he dodged Quick Man's beams of light, fought and defeated Quick Man (who was stated to be FTL in a manga though personally I'm not sure if that's canon to the Mega Man Classic series) and fought Duo who traveled from Jupiter to Earth in 38 seconds which, according to calculations, is 50x faster than light. He also outran Galaxy Man's and Saturn's miniature black holes and this is impressive since spaghettification didn't effect Mega Man. However, I suppose you're right about his running speed not being clear.
(And I just realized writing this comment was pointless, but screw it I'll put it up anyway.)