Depends on the tire, too. I tried 28 wide Conti 4000's on my bike (BMC says 28 is the widest tire I can fit). I started having clearance issues (on a disc bike, so it was hitting the frame). Checked the tires and they measured 32 on the rim. Had to go back to 25 wide (measured 26 on the rim). I have been told since that these tires seem to run wider than advertised. The new Conti 5000's apparently run closer to what they should.
That said, the bike was MUCH smoother on the 28 (really 32) tires at a lower pressure rather than these 25s.