If a milestone is important to you then the ones above are reasonable.
I however feel a really good horn will give you the desire to practice more and also will not limit you.
Many times I hear of young students having difficulties with range or flexibility which end up being a result of an inferior quality horn imposing limitations on their abilities due to design/manufacturing flaws.
Of course I'm not referrring to the Conn you mentioned and I have no Idea what your other horn is like so I cannot say this is what is going on in your case.
Bottom line, if you really want a better horn and can afford it go for it! Life is too short to play a crappy horn!