I am building a new PC for both productivity and gaming. I plan to play some games at 4k and others at 1080p. Which GPU would be the best option? The build is themes towards black and white, so I have been looking at the ASUS Dual 1070, but is a 1080 or 1080 Ti worth the cost? How long would it last before needing an upgrade and when should I buy (needs to be before Christmas)?