Wel lit depends on lots of things.
A couple of years ago I could do a reasonabe job of 6 MP image to A2.
As I type I'm printing a 6 MP image to 43" x 64.5" for a show in LA.
It looks pretty good.
Of course one could argue fine detail is missing if you look closely. The lens has limits.
The trick is to maximise the perceptual qualities so the viewer thinks the print simulates reality.
This requires a strategy based on perception as well as physics.
The first step is deconvolution to improve image resolution and remove as much as possible of the demosaicing.
Next is local contrast enhancement . There are a number of ways to approach this.
Then the light distribution is modified .
The tones can be redistributed with custom colour spaces.
Upsizing can be effected with beta spline , sinc etc - much better than bicubic.
The final sharpening strategy is critical, and depends on the paper , the enlargement and all the things that have gone on before.
All these edits use gradient masks in various opacitiess to directt the vision and create attenuation.
It takes a heap of research and practice to learn the moves and to apply them requires developing a strategy for each individual image. It's like chess really.
I have to say Photoshop is very limited in this and one must look at a lot of very specialist software.
The potential though, is very exciting. Needless to say i will not be reopening my dakroom