I've kind of been noticing that parallel limb bows aren't as affected by string add ons.....I'm not sure why that is either, or if it is....It's just something I've started noticing. I say that, but when I took the string silencers OFF my Vectrix I LOST 7 fps....So maybe it does......

Are you SURE the poundage was the same? The string may have stretched just a bit, slowing it down some.