The I-beam chase is fairly shallow, behind that is about 2.5 feet tall to the ceiling, so it won't be that hard to get big items like rocks in, but it's definitely close in the front. I don't think for a day to day access it would be any different than my old tank where the T5 fixture was ~8" off the water?
I went back and searched quite a bit, and came across this thread/poll:
https://www.reef2reef.com/threads/poll-display-stand-height.386757/
I watched Mark Levinson's podcast about stand height, and I agree with most of his comments; however I don't yet know how much of a pain it is going to be to have to get on a stand to work in the tank for anything but the very top of the rock work. I don't know if I'll have strong feelings until I get all the equipment underneath. I'm going to try and stick the equipment (sump, UV, chiller, skimmer) underneath and see how the clearance is. I'm coming off a stand that was only 30" tall, so it was a nightmare to work under the stand, so I went "tall" but the builders took that literally and didn't consider the extra height of the plywood and feet... If I shaved 2" off the stand, I'm not sure that is going to get me much more access inside the tank really.
Thanks all for the input, I hadn't considered the access with the lights.
FYI, this is what's above the tank, so have to be careful drilling!