My build was very close to yours, and I also have the Bora Ultra Twos and decided upon Continental Competitions for my first foray into the Tubular experience. I chose them because around where I ride a lot of people seem to like them and they just seemed like they'd be more durable to me, than say the Vittorias (I used the Vittoria EVO CX clinchers a lot before switching to Continental 4000s and definitely flatted or cut the Vittorias way more frequently than the 4000s). Anyway, at around 1300 miles, I got my first flat on the Contis. It was on the rear and was the result of something finally getting in the one and only little cut that I received early on. The tire was getting to the point of replacement anyway and I am not unhappy about the wear I received. I weigh close to 200lbs. The front is still fine and I'm going to use as a spare.
But on this site, there seems to be a lot of hate for the Conti Comps, at least when compared to the likes of say a Veloflex Carbon for example. So... today I just finished glueing up my first set of Veloflex Carbons on my Boras and am anxious to try them out this weekend. I'll keep track of the mileage, flats, etc. If I seem to get flats a lot more readily then I'd be very inclined to go back to the Competitions because they seemed fine to me, although admittedly my experience riding tubulars is pretty limited so far. Barring any freak punctures early on (they can happen to any tire), I'll keep track of the mileage on the Veloflex to see how they wear compared to the Contis.
I might try something from Vitorria next time in a slightly wider width next time (23-24mm), then decide on a favorite after that.
One things for sure, you can always change your tires down the road, so it's not the end of the world if you choose something durable for peace of mind while you enjoy your new ride. Then, down the road, you'll have something to look forward to in trying a really nice tire just for comparison sake and be able to decide for yourself which you prefer. Have fun.
Like I said before... looking forward to the finished build. I am excited for you.
Calnago, really love your build look at plenty pics of yours well done
Yes so far the 2 tubulars I am considering are the ones you have mentioned and thanks for the advice and not just bagging my choices so far, the Conti's seem weight wise a lot less and seem a very popular tyre both for the pro's and also general riders