I think the PM45 is going to be more enjoyable to shoot at the range and maybe easoer to shoot accurately, but the 40 is going to be easier to conceal.
For me, many guns have come and gone for CCW duty because they just didn't work out for concealment or ease of carry. Therefore the most important factor to me is concealment, which gives the PM40 the edge. I am also a .4 caliber guy and prefer heavy bullets. Thus the 40 beat the 9 for me.
Your preferences may vary, so the size difference may not be as significant a factor. In a life or death situation, recoil is going to be less of an issue, but how well you shoot the weapon will be very important.
When I started practicing with my PM40, it was strictly a close up last resort weapon, as I was not reliably accurate beyond 3yds. I have increased my effective semi-rapid fire range to 7-10yds now, but it certainly isn't a gun I would pick for home defense where my effective range needs to be 15yds. My point is that if you feel your defense scenario needs to include a longer range accuracy capability, you may want to consider a larger and possibly more controllable weapon...I.e. The PM45