1600x900
Oh, yeah - GTX 1070's definitely overkill for that; nevermind the GTX 1080! GTX 1070's even overkill for 1080p60FPS.
Hell, the 4GB 960 SC that I have does quite good at 1080p - i.e most games at Max settings for most games at 30FPS or 60FPS; FPS max depends per game.
Hmmm, I do wonder how my 4GB 960 performs at 900p; never tried. I'm a 1080p guy on this desktop. You might want to check some benchmarks. 4GB 960 performs very similar to the 2GB 960, but offers more VRAM buffer (for higher textures + higher settings) and often gets same to a few frames more per game.
Often, for me, w/ that 4GB 960 card, if in-game I've capped it out at 60FPS and say the performance is often b/t 30FPS and 60FPS, especially if it's bouncing up, down, around and whatnot - I'll add an additional 40FPS for my common middle ground that I just cap games around that via MSI Afterburner, afterwards. Usually, that 40FPS cap via Afterburner for me can stable a game out - or any other framerate that I can find a game often sticking at in most instances. Sometimes, though - I can do better than that, if a framerate for a certain game is commonly landing elsewhere (i.e. say 50FPS).
Still, I really wouldn't touch any older cards below 1000 series or below RX 480 (b/c these look like the biggest video card jump for ONE generations of cards in a very long time) - unless you can get those older cards ridiculously cheap in some kind of killer clearance sale, someone wants to sell it cheap to you, or (even better!) someone just flat-out gives it away to you.
If you still don't mind spending the $349-449, best reason to go for a 1070 at 900p60FPS, is to future-proof - especially for Max settings at 1440p60FPS + 4K at around 30FPS.
But, with AMD pushing the RX 480 at $200 - if you don't mind using AMD, you might want to wait for benchmarks and reviews on that RX 480. You could wait and see from there - and see if you'd rather invest in a GTX 1070 or 1080; or save money and go AMD with the RX 480.
On most newer AMD cards with DX12 games - in which, BTW there ain't many DX12 games yet (those currently require Windows 10), BTW - the Fury X will out-do any other card except GTX 1080; and we know Ashes of Singularity (DX12 game) is performing well on RX 480. It'll be interesting to see RX 480 performs against other DX11 games, b/c NVidia's always had the advantage there, with most of their recent line of cards.
