I also converted my MP40 to 9mm but I used a S&W factory barrel purchased from Midway USA for about $70. The Storm Lake conversion was a lot more expensive.
I shot the MP with both barrels back to back and I was slightly more accurate with the 9mm than the 40. I also tried the 40 cal mags...
M&P 22
I took my M&P 22 to the range for the first time earlier this week and it is a joy to shoot. I had 2 non shooters with me and 1 novice and we fired a lot of different guns but the M&P 22 was everyone's favorite.
I was really surprised at how accurate the new shooters were with this...