+3

As far as one tire being "slower" than another - it's all about rolling resistance and weight. The weight differential is negligable for a ruggid tire like the gatorskin (they weigh the same as the Vittorios mentioned) and the rolling resistance although slightly more for a kevlar belted tire is also negligable and can be offset with a few extra lbs pressure if you choose (and I don't). If these two items do make a difference to you then go get lighter wheels as well. I would rather have a ruggid tire on a fast descent or in a paceline and there are several out there that give you a good tradeoff and are considered good training tires - the gatorskin being one of several. I use to run GranPrix's which are more of a performance tire but they don't hold up as well. I could not see any speed difference on my standard training rides when I switched to the gatorskin - maybe I am just slow on everything. I have not tried the Vittorios but may when need new tires.