I would consider those Nashbar Streetwise neither skinny nor light.

I've got some 26x1.25" Panaracer T-Servs which roll really well. They weigh 240g each (claimed), and at 32mm wide are still one of the fattest slick tires I own. (Yes, I'm a weight weenie.)

That said, I'm not at all surprised that your average speed didn't change much. Lighter tires feel very different, and I personally believe that over a long enough ride you fatigue sooner with heavy tires, but the differences in actual speeds are minuscule, even in theory. Rolling resistance as a product of tire construction and rubber quality is often a much bigger factor than weight.