Chris I remember when you had this issue before......Im doing well BTW
Few things,
Being that it came back up points to a hardware issue.......As a hardware guy, medical device repair, I run into graphical errors often on our standardized workstations, its very unlikely a software issue would pop up like this....
If there was an issue on our end , due to how MAC's are standardized, we would see this very often.......What I mean is your iMAC has several identical versions out there running X-Pane 11 with SMP that do not have this problem. Nor have I ever seen this on my MBP.....
As far as it only popping up with SMP, best guess would be SMP does something different than the core program that your GPU cant handle due to some sort of defect....
With all that I have been proven wrong before, life is a learning process, but Im really confident this is outside of SMP.....