You can pick up the pace and we ain't talkin' salsa. REI's OXT Pace shirt has the oh-so-useful half-zip format we've come to love, and with one serious caveat, if you haven't tried half-zip pullovers the Pace could be a great introduction. It's a bit heavier than REI's Lightweight MTS long-sleeve zip-T for colder layering or lone-wear.
The caveat is this: the cut is really tight on the biceps, so you'll want to try this thing on first. I don't have the world's biggest guns but the Pace felt constricting and bunched up on my upper arms. If the cut works for you it has some nice extras that make it a great stand-alone piece: there are thumb-loops and an arm zipper pocket for small items. The loops are great for a little extra coverage on your hands when running or hiking, and they keep your cuffs down when pulling on gloves. The pocket has an interior headphone port.
The eminently breathable Pace has plenty of stretch thanks to the 9% Spandex weave and strategically placed pit gussets. There's a welcome bit of extra length in the hem and a full zip neck band with flap and zipper garage to protect your delicate neck-flesh. There's even a hang-loop inside, a nice bonus usually missing on these things. The Pace has reflective piping along the zipper and at the cuffs, but none on the back, so face into traffic or reap the WindStar.