Originally Posted by hokiefyd

The size of tire won't make the bike feel sluggish -- it's more the tire construction and materials. The stock Bontrager H5 tires are very heavy, non-flexible, and will ride poorly. Changing to the same tire in a 38mm won't really improve the ride or feel of the bike much (in terms of making it feel quicker). Changing to supple 45mm tires will make a huge improvement, and will be better than a less flexible 38mm tire. In short -- it's really the tire, not the size, that is the bigger influencer over how the bike feels.

There are some inexpensive tires that will ride pretty well. I use and recommend the Continental Speed Ride tires. They're labeled 42mm but are really more like 38mm on the wheel inflated. These would ride a lot better than the H5 tires in any size and they won't break the bank.