sizzling :
Your i7 has 8 threads unlike the i5's the OP and I have which have 4. The 2 games you mention can both use more than 4 threads. If he needs to plan for a certain budget and wants 144Hz you really need more than a 4 thread cpu in the latest games.
Also the difference between medium and max setting usually makes little difference to cpu load. Usually as you load up the gpu more with higher settings which reduces the fps the cpu load drops. CPU load is more directly related to target fps than game settings. Yes some settings do impact cpu load but not by much.
Yeah I know.
That's why I said for him to go ahead and get the GPU now and see how it does on the current machine playing what he plays.
Then if he wants more he can build a new one, he would lose nothing because he could transfer the GPU to the new build.
If he gets a GTX 1070 I think he can play pretty well, a 1060 might not be strong enough (Like the RX 480) if he pushes the settings way up.
I couldn't play Rise of The Tomb Raider on max settings with the RX 480 even in my I7 7700K machine.
The game killed it.... ROFL. So I keep it in the i7 870 box and it's fine for what I use it for these days.
But I do with my GTX 1080.
The reason why I really never liked mid range GPU's..... (I only got it for the I7 870 box to play the newest games)