I've got a Marin 4 Corners, which is basically a LHT for all practical purposes. Extra long chainstays, beefy steel frame, 36 hole rims. It's not light or nimble, but it IS plenty fast. I don't feel it slows me down at all. I've recently started doing some club rides with it. Fast tires make a world of difference.
I don't think this club is setting any land speed records...but I keep up comfortably at the 20-22mph cruising speed. Maybe I would feel different if I were in a morw hilly area, but even then 5-10 lbs isnt going to make or break you.
I do want a new bike though lol. It's totally overbuilt for anything other than loaded touring.