Since the aluminum D loops sits behind the arrow on the string (dead center) it is about the same as adding arrow weight. Figure 1 fps for every 3 or 4 grns of added arrow weight. My aluminum ultra nock weighs 36 grns (just weighed it). So after taking into acount what the brass nock weighs that you replaced you probably lose around 10 fps maybe a bit more.

Those big peep sights with the rubber tubing to align then, figure 10 to 16 fps depending on where the peep is located and how long the tubing is. They work very well for aligning the peep, but they cost you about twice the speed sometimes and are a bit noisier because of the tubing.

I have never seen string silencers cost 15 fps. It largly depends on where they are on the string, but I don't think they would cost you that much speed if they were down by your nock. I use the the yarn puff balls and they make almost no difference. The closer the silencers are to your axles, the less speed they will cost you. And if you get them in the right spot, you may even gain a couple fps.

The thing is with a hunting rig, sometimes you have to make sacrifices to get what you want. If you want a really quiet bow, sometimes you have to sacrifice a little speed. Same thing with the peep. If you like that peep, or can't seem to get another one to work correctly then use the one with the tubing to align it. Many deer have been taken with this set up. Just remember to change the tubing often. It's a bit startling when one lets go at full draw. Sure it costs you a little speed, but at least you know the peep will be where it needs to be when you draw on a deer.

You have several questions about peeps and nocks, I was going to just give my opinions here, but I think I will do it in the respective threads you have started.

Good luck,
Paul