I was thinking about a RRA 9mm upper, haven't done my research on either caliber though...just tossing around the idea.
I never really thought about it for the SHTF type scenarios, I think I got that covered with other rifles. I am really looking at it from the training side of things.Now thats a tough choice. I think its funny that you have dedicated upper and ammo listed as a pro and con for the 9mm though. I think I would lean towards the Spikes 22 for two reasons. Reason one is you can run it without a stock or receiver tube; which looks freaking awesome. Reason two is you can cheaply store 10K rounds of ammo for SHTF purposes, and the .22 LR is an effective round for small game such as squirrels and rabbits which would be important in a SHTF scenario. Also, if you ever went supressed, the Supressor for the 6.8 would work on the .22