for someone not trying to not to lose warranty, but 1900 on memory is excessive overlocking. if you cant restore stock bios when the card dies. then it will be difficult for manufacture to read the bios chip without totally disassembling card to read the bios chip.
As far as I know, clocks don't mess with warranty or lifespan of GPUs, the factors that can reduce lifespan are temperature and voltage, and I reduce both
The system is very stable with this clock
I don't fell confortable to do a bios mod with these cards, I didn't have any problems with polaris bios mod in the past, but with these 5700, I won't change for now