auto hotkey helps with any classs
BM hunter or havoc DH
I think there were a lot of good suggestions, but the most important being: it might not be as much what class you play, but how you are interacting with the game.
I main a brewmaster monk which has a high apm compared to most classes. On M Bot last night I was around 70 cpm. (For a nice comparison, our BM hunter had 44 cpm on the same fight.) I am able to sustain this by using a Logitech MMO mouse which has a built in modifier button. Another HUGE help is that I use the mouse scroll wheel for my main two abilities. So for nearly 50% of my casts I'm simply moving the mouse wheel forward or back. This is also nice for "spamming" an ability. No mashing of keys, just a nice smooth scrolling motion. I almost never need to move my left hand from the wasd keys. Another item which could help is a gamepad - I have a Logitech G13 that I use off and on. It helps with the ergonomics and gives you more options. On that thought, do you use a 10-key keyboard? My main one is without a numberpad so that my arms can be at a narrower angle while playing. It might also be worth considering the position of your body as you play. Do you lean back? Forward? Are your arms on your desk? The armrests of your chair? What angles are they?
A more extreme option (which I have not tried), is to setup WoW to use a console controller. There is an addon, ConsolePort, which allows you to map all of your movement & bindings and play using just a PS4/Xbox/etc controller. I haven't used it, but there are videos of people raiding with it.