Formation Face rims are very stiff but on the heavy side and probably won't accommodate a 38c tire.

If you're using a tire that big, you'll be better off with a Velocity Aileron. If you're unfamiliar, it's a relatively lightweight rim having a 25mm width that was originally designed for cross racing but has slowly been seeing a bit more road and track use. We stock them but they're not up on our site yet (we're hoping to get them up there this week).