Depends on the bow and where the item is on the string, and of course what it weighs.

If you put string silencers in the right place you won't lose any speed at all, might even gain few fps if you get lucky.

The biggest speed killer is a peep with rubber tubing. Next in my opinion would be kisser button in conjunction with a peep. You just don't need both its wasted weight in my opinion, and it's close enough to the center to really be noticed.

My opinion anyway.

And string loops do not change your draw length. If too long they can change your percieved draw length, but they do not actually change the draw length of your bow, they just change where your hand anchors to your face. Using a different release will do the same thing.

Paul