"My main reason for a compact single-stack is concealability(EDC). I've shot some Sigs and really like them, but haven't tried the p239 - it is obviously relatively heavy, but does it conceal well? The kel-tec looks good for summer carry here, but if I had enough confidence I would just go with the PM9 as it is pretty much the same size as the P3AT.....oh choices, choices-what to do.."
From this I gather that you like your K-40 but want something smaller and lighter, hence the plastic grip frame option. I know what you mean, I am a big K-9 fan but I would prefer a smaller and lighter carry gun as well but still in a major cal like 9mm.
Here is the bad news, I haven't found anything that is smaller and lighter than the Kahr K-9 that I would trust with my life. Kel-Tecs are all out because they are unreliable junk. The plastic Kahrs are also not very well made and the one I had was not reliable. The Glock 36 is freaking HUGE! I don't see how a gun that is only slightly smaller than my SIG 220 can be called "compact" The Bersas are good guns but they are only .380 not 9mm. The Maks are reliable but heavy and have poor sights and triggers. The Sig 239 is okay but the Kahr outclasses it and weighs the same and is slightly smaller anyway. The S&W 3913 is a great gun but larger than the K-40. The Roabaugh is very expensive but it looks like a good gun. I don't have any other info on that one however.
As you can tell, I have been down the same road as you. What do I carry when I feel my K-9 is a little too heavy? My S&W 642. It is the only thing smaller and lighter than a K-9 that trust. I would trust a Bersa 380 too probably.
Sorry but other than the snubby route, you are going to be playing a chance game on reliabilty when you go much smaller than a Kahr K-9/K-40.
