Why don't you get a hold of a pair and find out for yourself.

I can pick them up for $AUD20 each on special, $AUD30 normal price, and they probably go cheaper elsewhere, so it's not as though they are going to break your bank.

Machka has been using the 23C version for randonnees for years and has found them to be durable enough for rides up to 1200km. I've used them on and off along with Rubino Pros, Rubinos, and Gatorskins. To me the Ultra Sports represent good value, and more so for a training tyre.