Peter
The Ultras are certainly a proven bullet.
I really can't say whether a particular bullet likes a cut rifled barrel any more than a buttoned barrel. Shooter use, and win with, both. A great barrel is a great barrel, whether it is cut rifled, buttoned, has 3 grooves, 4 grooves, 6 grooves, funny shaped grrooves, or what ever.
One thing to consider is the reamer design, especially in the freebore length. Ultras, being a "double radius" bullet, tend to set up on the long side. The trend has been to shorten the freebore to the .035 range so the bullets don't stick out so far.
For what it is worth, I shoot Kriegers, which is a cut rifled barrel. Lately, I have chambered up some Bartliens for my friends, and they shoot quite well. As you know, the Bartlien is also cut rifled.
At the level we have to shoot at, barrels can become funny animals. A good shooter will score a really great barrel of a certain brand and configuration, and it seems that will be the "hot ticket" of the moment. The trend usually last untill some other shooter repeats the occurrance with an entirely different brand and configuration.
My advice would be to find out what top shooters are using, (and winning with), on a regular basis, get one, learn it, and avoid the "trend of the moment". In the end, you will probaly enjoymore success........jackie