It wouldn't sound as good if it's more than a full step or so in my opinion. It depends though in my opinion. The lower the deeper and lower it sounds obviously. I would still keep all songs half a step from original (Everything the same as for example let's say 2010 or something like that) and only lower certain parts of the song or certain words, etc.

If I made music I would keep everything half a step or just have them recorded in a suitable key from the beginning.

Weird thing is Jon once said that they also play their songs 1 BPM slower than original version cause it sounds better.. 1 BPM isn't noticeable I bet.