Timmy,
I have fired a friend's (all metal) Kahr in .40 S&W and my impression of it was that it was a vicious little.. er.. female dog. My friend does like to load his reloads hot but he doesn't exceed the maximum load as listed. The recoil was painful and it had a nasty torquey snap to it. It wasn't like a .357 in a Scandium Smith but it was unpleasant. One mag was enough for me and I was not impressed. I did then put the same load in my P-06 and it was a night and day difference. The 9mm version should be a bit milder. The Kahr did have a smooth Double action trigger though.
As far as the Polymer frames go, they are actually quite durable. The slide usually rides on steel rails embedded in the frame. The old saw about Glock's passing through a metal detector is fiction. There is quite a bit of metal in a Glock. The Aluminum frames are fine too. Remember the P226 with a quarter million rounds? With today's engineering, almost all guns from major manufacturers will hold up fine to wear and use that You and I would put them through.
If you're not averse to Polymer (Tactical Tupperware

); If you get a chance, try out S&W's M&P pistol. It is actually pretty ergonomic (for me at least) and shooting it was a pleasant experience. They come in many different sizes and they are striker fired like the Glock. I've shot versions in 9mm and .40. Other plastic framed pistols that I did not care for were Walthers P99 and Beretta's PX4. They all functioned fine but they felt too big in my hands. I can shoot them with no major issues but they don't feel as good as my SIG. The PX4 was OK (in .40) but I felt the recoil was excessive compared to my CZ P-06. The Springfield XD isn't too bad either. Keltec's polymer 9mm's are OK too. Good manufacturing techniques make them cheap, durable and light. SIG's polymer SP2022 is a nice full size pistol, well known for its smooth trigger. It has interchangeable grips so it can fit a variety of hands. The SP2022 is DA/SA and not striker fired though. It can be changed to Double Action only (DAO) as the entire fire control mechanism comes out as one assembly.
From SIG's site:
the SP2022 can easily be converted from a Double-Action/Single-Action to a Double-Action Only configuration through a unique integral fire control unit
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I did have a rather frustrating experience this afternoon. I went to a pin shoot and used my .40 in the big bore match. It just didn't have the authority to fling the pins off the three foot table. I will be looking at .45's or (grin) maybe a 10mm. The 10mm will allow me to use the same bullets that I use in my .40 which is a plus.
“Never give in, never give in, never; never; never; never – in nothing, great or small, large or petty – never give in except to convictions of honor and good sense” — Winston Churchill, Oct 29, 1941