http://www.fivesevenforum.com/
Do some reading on there. The "effectiveness" of the 5.7x28 has long been argued again and again. A .223 5.7x28 & .22 rimfire are all ".22's" technically speaking.
I've put plenty of rounds through my FiveSeven and love it. Dad carries his nearly every day as well.
Lots of charts and ballistics information & tests are being done on that forum.
I'm not going to try and sell you on the gun, as that is up to you to decide.
I've seen what happens when various rounds from the ss197 all the way through to some of the hottest (S4 Ultraptors) are shot into various test objects, (pork shoulders, 1/4" steel armor plates etc.) and would hate to be on the receiving end of that mess.
But, at the end of the day, you have to be comfortable and have trust in your weapon. I do, you may not.