Zoomify does all of that.
You do need to be able to host the images yourself though, and i think you would probably have to pay for the pro version to do the jpg overlay stuff, but it is not very expensive.
We regularly use this for gigapixel images, although none that i can share publicly, and it seems to place very little stress on the browser, even on mobile devices.
Worth a look anyway, and the free version has no limits on image size or unsightly watermarks all over the place if you just want to test it out.