I switched to a PowerColor R7 370 PCS+ and have the same problems as reported
already. Starting with radeon.dpm=0 or nomodeset helps to boot up.  I'm on
Fedora 23 at the moment with a 4.2 kernel version. The quirk_list fix (in my
case: { PCI_VENDOR_ID_ATI, 0x6811, 0x148c, 0x2356, <CORE_CLOCK>, <VRAM_CLOCK>}
) seems not to work, but I'll try some more values. I'll also add the vbios of
my card.