50 1.2 L and 50 1.4 from f5.6 to f16

The best lenses for this purpose would be the Canon 50f2.5 macro, Sigma 50f2.8 macro, or a similar macro lens. The Tokina 35f2.8 might work - but all of this depends on the size of the work you want to photograph.

Maybe it's just me, but I would be choosing a focal length longer than 50mm to reproduce art. You're going to get too much distortion at 50 mm in my opinion. It's going to make the edges and especially the corners look weird. I'm thinking the 100mm would work perfectly.

The appropriate length depends on the size of the art and the crop factor, if any, of the camera. In the film days, the best lens for this was the 50 macro. Now, the 50 may be long on a crop - for large, flat art pieces. If you are trying to photograph a 3'X4' painting, you don't want a long lens.
Distortion is not an issue with a flat field lens like the Canon 50f2.5.
Personally, I have the Sigma 50f2.8 and Canon 100f2.8 macro lenses, but expect to use the Sigma for my wife's art.

From www.slrgear.com regarding the EF 50mm 1.4

Except that it's not - not at MFD and not at infinity. Look at the ZE 50 MP comparison on the previous page. Plus it's color rendition is just awful. In short the EF 50/1.4 is definitely not a good choice for art reproduction.