I can't speak to the SR40, as I've only shot the SR9 and SR9c, but I did enjoy the platform in 9mm in my limited experience with it. I don't know how the SR40 shoots, and I also haven't talked to anyone in person who has shot it yet. I can't say I know what the internet consensus on it is, either.
I typically favor 9mm (or .45) to .40 by a little, but I also think that .40 is where the recoil-dampening effects of the PX4 platform's rotating-barrel action really shine. The PX4 pistols (aside from the Subcompact) are softer-shooting than any other comparable polymer-framed service pistol in each of its respective calibers, in my experience, and I think the difference between the PX4 and others is most noticeable in .40. When I get around to buying a PX4, it will most definitely be in .40 (and then later in 9mm
). I still think it's awesome in 9mm, though.
So, I would vote for the SR9/SR9c and the PX4 in .40.