It is interesting to read this post. First, I can verify the issue is not limited to Asus brand on the 280x. I order an Asus card during Christmas week. I really like the card overall, and the following week placed an order for a 2nd card. As I was using the first card during time off, I started seeing these artifacts during high useage. I RMA'd it back to Newegg the day I received the 2nd card. I have seen no issues with 2nd card. Due to inventory issues, Newegg gave me a refund instead of replacement. After a week with out of stocks, I ordered a Sapphire Toxic. It is the first none Asus gfx card in over 12 years. It has minor artifacts as well. I am thinking it is a driver problem myself. When the artifacts occur on the toxic, I can just refresh screen and it clears up. It does not happened very often. I am going to put it to some games this weekend to determine if I am going to RMA it as well. If I do, I am going to request cross ship, so I know that I have a card coming.
Asus Maximus VI Formula LGA 1150
Intel i7-4770K
G.Skill Sniper Series 16GB (2x8GB) DDR3 2400
Asus R9-280X DC2T-3GD5
Corsair Force Series GT 120GB SATA III SSD
Asus VE248Q Black 24" 2ms LED
Cooler Master HAF Stacker Modular Tower
OCZ ZX Series 1000W Fully-Modular 80Plus Gold