What a beast! Nice fit. Looks like you've got a nice volume of air in that tyre vs. the 1.75. Looked up and the front is just under 200g more than the Marathon Plus which isn't much more for added comfort, durability and reliability. Love the old vernier calipers too! Good luck with the back one. :)
I'm guessing your tyres are being stressed a lot more than ours with using it for your work? Mostly we have a 28kg child with stuff in it (sometimes x2), but then it does the weekly shop and also we shift loads of other random items about we can get in/on it. It is garaged so out of the sun which I'm sure doesn't do tyres any favours.
We've yet to have any failures/punctures on our Marathon Plus's in almost 5 years, but I do regularly pull stuff out that's embedded itself into the tread. I did buy a Big Ben for more air cushioning up front, but never fitted as it offers less puncture resistance and the sidewalls didn't feel as resilient as the Plus.