If you're going to be hanging on to the rock bare-handed, do you really need gloves for belaying?
Of course, I'm one of the very few people who insist you need gloves for belaying year-round, but not because of warmth. I use the somewhat pricey but totally bombproof Metolius 3/4 length finger belay gloves for summer and winter rock-climbing. Metolius also makes full-finger versions
, one of which has a thin tricot lining for warmth. I can't imagine needing more than that for conditions that still allow for bare-handed climbing.
I'd beware of mountaineering gloves like the BD Jetstream, which are nice for what they are meant for, but really don't fit the bill for intensive handling of ropes, especially double ropes. Rapelling and double-rope handling frequently involve having a finger between the ropes, and gloves made of soft fleece with no leather protection in the fingers are going to wear fast.
You can upgrade to a $70-$80 pair of ice-climbing gloves, which is fine if you'll also use them for ice-climbing, but that seems like too much money to me for belay gloves for 40 degree days.