Does too high "B-tension" increase wear This answer suggests that having B-tension adjusted so that the chain sits far from the cogs increases wear. Can anyone cite a source that says that? Experimental evidence would be preferable, but a statement from an expert would suffice. 

Sheldon notably doesn't mention it, instead saying that proper B-screw adjustment leads to quicker shifting, so I'm wondering if it's really the case.
FWIW, the mechanical engineering analysis that I have read about the mechanics of chains states that almost all the load is spread across the first 3 links that are in contact with the sprocket. So as long as you have 3 links in contact with the sprocket, you aren't increasing the load. 

But this is all largely arguing in a vacuum. Set your bike up so that it shifts well, check the chain wear frequently and replace the chain when it starts to show signs of wear. Gears don't "wear" significantly until the chain starts to wear and elongate and increase stress on the gears. If you always have a "fresh" chain, your gear cluster will last a very long time, 
regardless of how the B-tension is adjusted.