Chief,
I didn' t even bother to check speeds with and without these installed......I would expect very little speed loss with the Vibrablocks ( I guess I should check just to be sure someday) I scrap the Vibrablocks in favor of the SIMS Limbsavers because my target bows are only gonna have one or the other and the Limbsavers work better IMO. I' m sure you' ll get added vibration reduction if you had both, but who wants all that rubber stuff on those pretty limbs!? [:' (]