I use the PRO-45 for theater stage, I'm generally happy with them, for the price. One thing I've noticed is that they're very sensitive: sometimes during black (no light, short change of scene, silence at public and on scene) they're picking even the whisperings of actors _behind_ the scene, inaudible to the room audience.
I always hang and remove them after the show, even if the next show is tomorrow.
By specs it seems the higher-end Audio-Technicas have wider frequency response, more dynamic range. Probably useful for music and choirs, but not for voice I guess.
The PRO-45 comes in a small (~5") carton box, not solid. I wish I had a solid box.
I've used them for 2 years now and if I knew they were going to see so much use I think I would have bought the higher end ATs. But then, for higher end, one can go as high as hanging Schoeps capsules.
I'm not a professional, not much audio experience other than that, I don't know other mics.