Mmm, his crossing is not the greatest but the thing is he always creates more space for his crosses because defenders don't know which way he is going to go. He also has an enormous amount of involvement in the game. You know how we sometimes complain that Martial looks sluggish and not involved in the game. I've hardly ever seen a game like that for Perisic. He is very industrious, he is constantly making runs and is always on the move.
As a result, he receives the ball a lot in the final 3rd and puts a lot of balls in the box because he can always make space for a cross. A bad game for Perisic is one where he's put 10 balls in the box and doesn't find the strike once. He can be frustrating as feck like that, that's what the highlight reels won't show you, but you can't say he's not involved in the game. On another day he'll notch 2 assists off these crosses. If the striker is in tune with him he will get a lot of service.
As for being faster than Martial, it depends what we mean by faster. Perisic is pretty skinny and has better acceleration than Martial. But Martial is more muscular so I would expect faster top speed perhaps. That's what it seems like anyway. Acceleration is more useful than top speed when it comes to dribbling, though.