I had much better results shooting .40 S&W in my SIG 229 than I did in my S&W M&P .40 Compact. I finally got rid of the M&P, as I found it uncomfortable to shoot in that caliber. Currently I have five 3rd GEN 9MM S&Ws and a SIG 225 in 9MM. My only .40 cal is the SIG 229. I have no problems with shooting 45ACP in my Kimbers. I just found the M&P compact a bit too "Snappy". If I was going to continue to pursue a 40 cal in S&W, I'd look for a 4006. I think the added weight and barrel length would be make it a nice gun to shoot in that cal.
All in all, I'll likely move out of the 40 cal arena and stick with just 9MM and 45ACP. (Got a lot of 40 cal ammo to burn through in the mean time....)