I know nothing about Stihl saws (except that I absolutely do not want one, so I do not care about them), but I DO live over 7000 feet up, so I have some experience with the altitude.
I do not think you should worry too much about the limiter caps on current saws, every single one of them must have a way to remove the limiters and properly tune the machine. I do not think I will ever want a saw that thinks it can do this itself - just more over-priced, complicated and unneeded crap. Any decent dealer should be able to quickly and easily do this for you, and if you find one so stupid that he claims it is not needed, well . . . they ain't one of the decent ones!
My favorite mid-size saw that is also great at high altitude is the Echo 590/600/620 (all pretty much the same saw). The limiter caps are very easy to remove, neither the engine nor the exhaust needs modification (IMHO), and the saw is easy to tune for anyone with basic competence. Although I dearly love my CS-590, I would recommend the CS-620 instead for altitude.
The CS-590 has a somewhat unique carb that includes a combined high-speed carb circuit that utilizes both a typical H tuning screw AND a fixed bypass circuit that prevents some idiot from leaning out the saw so bad it burns up. Unfortunately, at 7,400 or higher, that fixed bypass circuit actually prevents you from leaning out the saw enough; I can get very close to the specified WOT RPM, but not quite. I think it is totally fine for 7000-8000 feet, but I wonder if it would be acceptable at 9000? I have not tried it that high, so I can only wonder. The CS-620 is a 'pro' version of the same saw, and one of the very minor changes to it is a different carburetor. That might justify the additional cost for real high-altitude use.
EDIT: a general apology to all for replying to this ANCIENT thread - I do not like to necro-post, but I did not notice the original dates. I sure wish they were more obvious on this forum!
Zombie thread alert!!
Damn...8 years, thats a good one...