Speed loss from the rubber tubing will vary, depending on several factors. It can be significant. Whether your peep will turn without the tubing, will depend on the quality of the string you have on your bow. Anything that is attached to the string will slow the arrow. The closer to the nocking point, the more a given weight will slow the arrow. Peep weight can vary considerably, therefore so will speed loss. Most only affect speed by a few fps, if they don't have the rubber tubing, but it can be more.

In the past, tons of peeps with the rubber tubing were sold. They were necessary because strings were poor quality and peeps would constantly turn. That can be prevented with today's strings, at least the well-made ones. I would recommend getting a custom string if your peep turns without the tubing. The noise factor from the tubing slap, is just too much for my tastes.