Well, I'd say if you're truly a pro and editing 4k and panoramics with that high of a level of scrutiny then you need the right tools to do your job and you don't have them. So stop being cheap, invest in the proper tools and amortize your costs over the life span of your expenditures and factor that as a business expense, write it off on your taxes and gain more work to offset your outlays.
I know plenty of pros who do quite well with color management on iMacs. I make pretty decent prints using my 2008 iMac and Epson 3880, but I don't sell them as a rule. I do, however, create art pieces that I sell and the color of my final product is good enough for me.