I do not know what kind of games that you play but if a nVidia GTX970 is not good enough so you think that you need a newer GPU then you probably play games that requires would also require a better CPU also... (?)
Anyway , like you then I prefer Intel CPU and nVidia GPU , but I personally do not understand the budget choice of i5 over i7 if building a new PC , surely you will save some money but looking at the greater picture and how much money one spends then I wouldn't buy i5 , though you have probably been happy with yours , I would go with an i7 like one of these :
https://www.newegg.com/global/fi/Product/ProductList.aspx?Submit=ENE&IsNodeId=1&N=100779907%2050001157%20601295136%20601304866&Manufactory=1157 on a suitable quality board of your choice , that will require new RAMs also I think
Then of course whatever nVidia GPU that you think is needed....
Personally find the weak point of your present PC is the CPU and not so much the GPU , but you may play a lot of FPS games at high frame rates and so on and I don't , and if I play anything resembling FPS games then I play at lower resolutions than many other people and lower frame rates .
(My present setup is an i7 (6700 Skylake generation) and a GTX 760 with 4GB RAM)
(my only reason for not buying the 6700K and a GTX 770/780 back then were the higher power consumption , I looked at the electricity bill and went for the lower daily costs since I tend to have my PC running many hours day in and day out , had I been able to find a "green version" of the GTX770 back then I would have bought that instead - most people will find choices odd however I do not care , I am happy with my PC and do not consider upgrading it before I want to play any games that would warrant it. One ought to buy CPU and graphics card tailored to own preferences more than to others and I personally tend to emphasize CPU power more than GPU power)