A few thoughts... I think this is a very strange decision from Razer. I'm asking a few questions here, will an 860M allow you to game at 1080p with any sort of reasonable settings? And will an 870M allow you to game at 3200 x 1800? Would an 860M? No, but the point I'm trying to make is that I don't think people would game at the native resolution of the 14" Blade regardless of whether Razer went with a 860M or 870M. To me the ideal gaming resolution for that situation would be a clean quarter res, which the 14" Blade allows for (1600 x 900). I really think the 860M would've been a better choice given the display and form factor in that situation. This 17" model doesn't really allow for that. You could certainly turn the resolution down to 1600 x 900, or maybe even 1280 x 720, but not without artifacting as a result of the displays native resolution. So ideally you'd want to run this 1080p display at 1080p, in which case an 870M probably would've been the better choice, and it almost certainly would've made a bigger difference here than it does at 3200 x 1800.
And then there's the fact that Razer threw a lower res display and lower TDP GPU into a larger higher TDP form factor, but whatever.