I think I'd go with a 3gb 1060. You want the extra performance of a 1060 over something like a 1050 Ti. There are still many games that will use all the videocard power you can throw at them.
I think the value of 6gb vram is substantially reduced using an older i5. The kinds of games that need more than the 3gb vram will mostly also need more than an i5 2400.
So, as always, it depends on the games.
I would not advise an upgrade to an i7 2600 unless you have definitive proof that it would actually help. IF the card you are using can benefit, IF the games you play can benefit, and IF you can find one for a decent price, then sure. The point is that you don't want to sink too much money into this old of a system. A good videocard? Sure...