Unless you're allergic to the materials or just absolutely cannot stand skintight clothing (like me) to the best of my knowledge proper compression clothing will give you a noticeable if not necessarily substantial mechanical advantage. Something to do with muscle vibration or somesuch, I assume the usual sources would have more information.

If you do decide you don't like tight stuff though you're not completely out of the game for modern stuffs, my biking shirt is a non-elastic moisture wicking sport shirt that fits like a nice breathable slightly baggy tshirt. Just don't go too baggy, like someone said further up once you get past a certain point you're basically wearing a parachute. I have actually been yanked off of my bike before when a strong wind catches my jacket.