I'm trying to decide between the two.
The only real downside to the Ultra is that at 7lbs it seems heavy for a rimfire (it also is SLIGHTLY more expensive and SLIGHTLY longer than the Sportster, but those factors aren't significant).
On the other hand, I'm wondering how much of an advantage the heavy barrel is. How fast does a .22 Mag rifle barrel heat up when shooting groups at the range?
If the heavy barrel saves me from having to wait 5 min between 100yd shots to get good accuracy, then that would be the deciding factor. However, if the standard .22 Mag barrel can shoot good 3 or 5 shot 100yd groups without waiting between shots, then I'd purchase the Sportster.