Excellent informative post, thank you!
Good timing also as my son just got home from college and we're going to dust off and update the old milk crate mining rig we used on X11 2 years ago.
To give you an idea of that mining period it's made up of 2 x 5850s and 1 x 7850 so those obviously need to come out. I have an XFX R9 390x to pop in it but not quite sure what 2 additional cards is the best ROI at this moment to buy. Based on today's prices can you make me a suggestion please?