4k is worth the price increase. IMO the systems are a wash, both are awesome. If you plan to play online, pick the one more of your friends have. Or browse exclusive games and go with what's appealing.
I've failed the last two years of finding a PS4 Slim on Black Friday due to laziness. This year I'm hearing there will be nice deals on the Pro since the 5 is out next year, so I'm going to wake my ass up early on the 29th.