Mixing 2x4gb + 2x8gb Kingston Fury Ram

[tsumannai]

I originally had a 2x4gb kit of Kingston hyperx fury (cl10) of ram and then thought to upgrade it to the 2x8gb version. I firstly put them both into their respective channels with the 8gb in the primary channel. It managed to boot luckily so my system apparently now has 24gb of ram. Then In the Asus-Bios i set the ram frequency to 2200Mhz. (i don't know much about ram overclocking.)
1. Is there a way to test the stability of this
2. Are the benchmarks Ok for this setup?
3. Should I even be doing this at all?

I've linked some screenshots here (Maxxmem2 and CPU-Z)

 

[sammy sung]

You can create a bootable memtest thumb drive. Leave it running for a few passes. If all checks it's most likely stable. To be perfectly certain I'd leave it running for 12-24hrs. I've seen dimms pass over 80x then error.

http://www.memtest86.com/download.htm