I've had poor results with overclocking the 4 GB Sapphire Nitro+ 480s. I believe they have slower RAM than the 8 GB version though. Is it stock 2000 Mhz on the 8 GB version ?
I don't think you will be able to overclock to 2100 - maybe try stock setting and see if it is more stable.
I would try a slower GPU clock setting and lower GPU and RAM voltage - I think I had mine running at:
-cclock 1150 -mclock 1850 -mvddc 950 -cvddc 950
Try yours at -mclock 2000 and work from there.
i have 1750 timings in custum bios , cclock is 1200 and cvddc 990 , mclock 2150 and mvddc is 1000 , normally this would crash my windows but i wrote a script that the desktop reboots every
30 minutes, like this i can mine at a good speed, and less power consumtion. and to the chance of crashing the system is much lower ... ok 48 restarts in a day is not so nice , but i think it is worth it