I've only done four man runs so far but it's great, no problem.

I can imagine only having up and down to quickly heal other party members could be a bit harder scrolling through a eight man list, but you should have another healer helping you so it should not be an issue.

I'd also love to hear from someone who had done eight mans with a gamepad. I also play on PC so I guess I could make the mouse work but so far I've been exclusively controller on both systems.