Not sure if there's a solid answer that can succinctly compare drunk and sober pieces, but here's a little info on some of van Gogh's most famous works.

In this letter to his brother Theo, van Gogh talks a little about his composition of his postman series and The Night Cafe.

It seems that while the postman was sitting for at least some of the portraits, he refused payment, but to van Gogh's frustration, "the good fellow, as he would not accept money, cost more eating and drinking with me..." So apparently they were drinking together as he painted (this doesn't necessarily mean he was drunk though).

The Night Cafe is a little different. Often, it's interpreted as a representation of the sensation of going mad- the image is skewed, with an unusual perspective and an almost spectral bartender (in the white). But possibly an aspect of this also has to do with drunkenness, as the setting is a place where people can "take refuge... when they have no money to pay for a lodging, or are too drunk to be taken in" (according to van Gogh). I believe he lived just upstairs and often visited the place in his depression. He also stated in this letter that he painted it during the night, so I would not be surprised if he was drinking with the other 'patrons' while he worked. So, it's possible to say that the blurry lights and warped floor are in part inspired by the dreary/drunken atmosphere of the joint and not just his deep melancholy.

Several times van Gogh compared The Night Cafe to The Potato Eaters. However I can't find any evidence that he was sober or drunk while composing it, so I hesitate to draw comparisons in those terms.