I have a friend who has all the good factory flash files from the C6.6 to the C32. I asked about flashing my 475 MXS with the 625hp file and he said "yes but it won't run better and will drink fuel". He's the one that explained to me which files work and which files don't.
Cat won't flash your 475 above 550 because to meet the emission standards you have to swap pistons, injectors and the top charger on a MXS to go above 600/625hp. Swapping these parts do NOTHING for performance it's all to make the EPA happy. You can easily get 900hp with just the 475 parts you have now. To get above that it's just an injector swap and a hotter tune.
Also most of the "heavy haul" files just give you more RPM, like 2300 instead of 2100. There is no added fuel vs the normal 550 flash. With an Acert you have no other option other than aftermarket. You can't change injector trim codes on an acert either, if anyone tells you otherwise they have no idea what they're talking about.
If your near Ohio I've got two tuned 6NZ's and a tuned MXS Acert you can drive that will settle the discussion. I strongly suggest if your MXS has not been re-flashed since it was new DO NOT have Cat flash it. I guarantee you it will run worse with the "new" 550hp file than it does with the 475 file that's in it! Set 1/2 of your $399 on fire, you'll be better off.