Also these days I guess even 5MB images won’t hurt anyone.
I don't really see the point. The largest image I have posted, is still under 2 MB. There's no point embedding larger images. If you really need a higher resolution, add a link.
I can try asking @theymos to adjust the image proxy to 3MB, which would even give more freedom. 
That doesn't help. I forgot why you increased the limit from 2.5 MB to 3 MB, but this image should have been 1.4 MB so none of this is a solution.I wonder what sort of image would need to be 5mb? I mean we dont need to be posting
large files like that, maybe on a photography website where people would be "pixel peeping".
And if accessing the forum through smartphone it enables us to zoom in if required for
more detail.
Essentially extra data means extra costs for storage.