I apologize if this has come up before, I tried searching but could not find a thread regarding it. Anyway, I've recently purchased a SUB-2000 Gen 2 in 9mm, yet Kel-Tec will swap out the 9mm hardware, barrel, etc. for a small fee to the larger round. I've looked up most any kind of video/article regarding the two, yet cannot come to a decision on whether to keep it 9mm, or to upsize to the .40cal. I have no other 9mm guns in my collection, yet a few .40cal (if that makes a difference). If anyone has any info, or an opinion, please feel free to post a reply. Thank you in advance!