Why The R9 290 & Other Select Radeon GPUs Are Performing Miserably On Linux 4.7

With this weekend's 5-Way Mesa 12.1-dev + Linux 4.7 Git Radeon Comparison and other tests I've done on Linux 4.7 Git with Radeon hardware, the R9 290 has regressed to the point of performing noticeably worse than other AMD GCN GPUs... Many other Phoronix readers with different Rx 200/300 graphics cards have also confirmed their graphics cards performing poorly on Linux 4.7...