I have a set of ultegra 6800's. They're solid, smooth and light. No complaints other than the aforementioned tight tire fit. (Getting a brand new set of GP4000II's on them was a challenge)
I've used them as a backup/training wheelset on my CX bike too. They have taken a fair amount of abuse with no signs of wear.
I can't imagine finding a better bang-for-the-buck wheelset right now.