Just to make sure everyone's on the same page... Helium is 15*F, Summerlite is 32*F...
A lot of it is so personal... Kind of depends on how you like to sleep, too. I hate being cold at night and tend to error on the side of a warmer bag. Recently, though, I've used a 30*F bag even for temps around freezing. With a down vest or jacket it's been fine.
Also kind of depends on solo vs traveling with someone; slightly more safety margin with another in the mountains. (Not meant as a solo-travel flame, I've done a lot of it, too.)
I think if you're uneasy about whether or not the 30* bag is warm enough, then you should probably bring the warmer bag. If it's more of a "Hmmm, I wonder..." question, I'd probably roll with the 30* bag. Personally I'd probably take the warmer bag on a trip in the mountains.