Ruth, Bonds, McGwire and Sosa.
If I could figure out a way to get 1st half numbers I would've done that. But even without it, I think that list is pretty illustrative.
Here's another...from 1950 to 1993, here's a list of players who had full seasons of .350 ISO or better:
1961 Mantle (.370)
1956 Mantle (.353)
1961 Maris (.351)
From 1994 to the present (including Chris Davis), there have been 22 seasons of .350 or better. Many of those seasons belong to individuals who have been speculated about, either wildly or non-wildly.
I'm not sure if questioning the performance in this day would constitute wild speculation, especially when we have a long history of seeing what the human body can achieve in the game of baseball. We have seen what PED usage can help someone achieve. It doesn't take a rocket scientist to put the two together and say "Hey, maybe something is going on here".