Re: Upgrading to a new horn...
Hey, I'm in your same position. I'm a sophomore too and the Jupiter is getting a litte worn. Believe me, I'm no expert, but of the horns you have listed, the Mark VI is the most reputable. (notice I did not say best, because I have never tried one) Only problem is that its extremely expensive, and probably too good for me! I don't really deserve that kind of a horn, especially with the wear and tear that my high school playing would put on it. I wouldn't be ready for it yet.
Now, that's just me. You could be totally different and way more advanced than me. I'd just rather stick with something I wouldn't have to be all jumpy about. (My friend has a Bach Strat. Trumpet and he is sooooo protective of it.) Hope I could help,