Alot of people can claim that here. And I shown professionals in other fields that they wrong on something they should have known.
All a professional means is you get a paycheck for your work, its not a grantee you are actually worth the paycheck.
Claiming you are a professional on a internet forum does not mean squat.
Final print is the product were going for as this isn’t going to someones PC wallpaper, were speaking of a end product print that somehow gets applies to someones arcade stick.
Forcing the DPI to a higher number actually makes the picture smaller (as you already state). So we have to counter with a even bigger image. Makes me wonder why you chose only 4mp or higher for your image search.
And yes I know what a megapixle is, its a stupid concept created by marketing. Its what should be ignored and instead you look at the image resolution.
And what is the formula you speak of Mr Professional?