Older CR pegs are 8mm and 8mm not 12mm. We are talking about the BOLT diameter not the head/wrench size right? And they are threaded into just aluminum...not a ton of tensil in that. I personally thing that pic of the ktmklx sanjoh posted is more than enough for average NON triple jumping stuff. JMHO though, and I have been called an idiot....no savant attached to it.
If you are cantilevering the peg mount very far down and forward, especially down, then yes I would add a gusset maybe at a 45* angle back up under to the frame, or if it is a clear shot, then all the way accross to the other peg even to balance out load.