On Comps vs Carbons - first - I've got a different point of view than what I mostly read. So keep in mind, this is largely on 303 Firecrest, laced to White Industry T11s, on a Baum Coretto, I weigh about 72kg, and I ride in and around the San Francisco Bay Area (crap roads).
Comps - I like the ride quality - I don't consider them "dead" like others seem to. They do "mute" the ride a bit - but on our roads that actually comes across as absorbing more road chatter, so it's more comfortable. G+s - I found to also be comfortable, but more supple as well. Carbons - I actually like their ride quality on our road the least. For whatever reason, they transmit more chatter. They are supple - and on smooth pavement they're great - but we have a lot of either a) big bumps or b) rough pavement. Net: Early read is G+ the best, then Conti Comp, then Veloflex.
Comps - great! It went flat early in its life in the rain - I couldn't find the puncture. I threw some Stans in. It was fine fro another ~3.5k miles. Still had the dimpled tread when I removed it (it had become reasonably cut up from the amount of glass we have). Rear tires lasted maybe 1.5-2k miles, which is pretty good. I'd say it lost the dimples at about 1.2k miles. I replaced it when it flatted due to a puncture from road debris (not glass). I assumed it was a sign the tread had worn too thin. Veloflex - I'd say the rear lasts more like 1.2k miles - maybe 30% less than the Comp. Its rubber is definitely more fragile. Center tread gone by maybe 900 miles. I generally found them to be good about not puncturing and Stans always worked great in them when I did puncture. Net: a wash.
All three have been acceptable. Can't say I wouldn't ride any due to wet weather performance. Right or wrong, my perception is the Contis have a slight edge over the other two - but I have nothing great to back that up (other than the apparent Team Sky switch).
All 3 seem totally acceptable.
The Veloflex and G+ are easy, the Conti is torture.
Speed / rolling resistance:
I doubt this is human detectable
Net: I'd definitely not ruin a new / lots of life remaining pair of Contis to switch to the Veloflex. They're both good. If they were equally easy to mount, I'd use the Contis over the Veloflex. I've got to get lots more miles on the G+ to know where I rank it overall - durability's a big deal for me. One short ride in I'm really liking the G+. But have I mentioned how painful it is to mount the Contis?