Oh boy, you guys keep coming, what is hard to understand in my posts or in "Mindinversion" accurate description that shamed the incredule replies above ?
What is an el capitan forum ?! Since you asked about reddit, and actual MBP users might be undeterred due to the noise in this thread (such as misguided BasicGreatGuy above) here are the other Radeons burned by El Capitan beta that I found in minutes:
https://www.reddit.com/r/osx/comments/392v2g/beta_testing_os_x_1011_el_capitan/csyl055
https://www.reddit.com/r/applehelp_...bp_early_2011_hangs_midboot_after_el_capitan/
https://www.reddit.com/r/apple/comments/3db8fw/el_capitan_public_beta_fried_my_macbook_pro_2011/
You're welcome.
Now I will leave you to it, deface the thread however you see fit.
You link two threads with not much response in them and most responses are the same as here. (that it is NOT El Capitan and that it IS hardware for those specific models.)
The third link you provided is your own thread on reddit. So I really wouldn't say "The Radeons fried by El Capitan public beta installation are piling on reddit.com right now" when that is so far from the truth and your links prove that.