Do you have experience with RMC? Do you have threaders and benders already? Would it be possible to sub out an install to an electrical contractor to get a feel for how long it takes them? If you don't have experience with rigid you'll be learning on the job and take longer at first, and you probably don't want to charge your customer for your learning, especially if you do a lot of work for them in your core competency (controls).
We usually estimate conduit/wire installs on a machine by figuring out how many guys we can use per day, and how many days it will take. That gives us a total labor hours number. Depending on the machine size, 2 or 3 guys may be all that can work on it without tripping over each other, or standing around. Usually you can have 1 cutting and threading, one or two guys mounting conduit and fittings. If there's overhead work, you want someone feeding material to the guys on the lift so they don't waste time coming up and down. Once you get wire pulled, if the cabinet is not a 2 door or larger, you can really only have 1 guy landing wires. The others can connect field devices. Then it is a question of how many days to land all the wires in the cabinet and how many days to connect devices.
Sorry if I'm telling you something you already know, but I have tried to come up with a scientific method like what you're asking, and haven't been able to yet. The part that's on your side is that industrial seems to be more forgiving/less cutthroat than commercial and especially residential, so you don't have to account for every wire nut. The recurring theme that I see here is that guys tend to estimate the labor low if nothing else. Just getting tools and material into and out of some plants can be a large time sink. Plus working around active processes, required safety permitting, etc, can eat up more time yet.
