[EricH]

You're trying to move twice the air through the same opening. That's going to have an effect; your actuation will be slowed down somewhat, as only so much air can get through at the same time, and you have the same pressure to push air through with. For, say, a 3/4" bore/1" stroke cylinder, like might be used for shifting, that effect would be negligible. But when you get to more of a 1/5" bore, 12" cylinder, say, there will be a noticeable effect on speed.