Since this is for a fixed installation, the choice you make is probably non-critical. Although the metro area and total number of simultaneous RF channels may modify that.
IMPORTANT: Do NOT be influenced by the products you see used on award shows. This is actually a quasi-random mix of rider preferences, endorsement requirements, and personal/technical preferences of the production staff.
That said, the fact that the Big 3 (A-T, Sennheiser, Shure) are the only ones you see does at least tell you that any of them is likely up to the task. There's too much at stake to use anything dicey.
Personally, I regard this as a two-horse race in terms of the technical abilities of the top systems from these manufacturers. And those two horses are Shure and Sennheiser. This is especially true in terms of computer monitoring, frequency selection/agility, etc.
Now, is the AT 5000 competitive in terms of sound quality, reliability and features you are likely to need? Yes, absolutely. As you can see in this thread, there are plenty of happy AT users out there. But when the price difference is that huge, it's for a reason. TANSTAAFL.