This would be the same dillemma I have few weeks ago. I would share a bit of my insights. It's actually depend on your usage, are you gaming enthusiast? If Yes, get the 970M. If you're gamer and wanted future proof then 970M as well.

Skylake is better cooling with enable more future proof of DRR4 ram. But all these doesn't play much role when come to gaming performance. Cost wise also 970M is more expensive. In the end, it is all depend on how high the graphic you want to play your game.

The best future proof combo is i7 6700 + 6gb 970M which I once wanted to upgrade to that cost around RM 6k which set me back a little.

960 should be fine for casual gaming.

If you going to play games in ultra setting, suggest you take 970.

Not really sure, but I heard from others that 970 6gb performance is twice of 960 4gb.

I haven't get my skylake with 960M yet. Couldn't commend much. 970M is more than 60% performance compared to 960M. What is coming out the next 3/4 years no one knows best, what can be sure is 970M will be able to play better graphic setting than 960M is for sure.

Like I mentioned Z5 Skylake with 970M should be quite a beast that can last for sometime if you able to fork out around 5.6k