My system can run gtx1070

Solution
Getting an i5 8500 would requite a motherboard upgrade too.

I would also say it's better to get a GTX 1060 with the i3.

Get the GTX 1070 if you plan to upgrade to a good i5 at some time and be aware that you won't be able to utilize the GTX 1070 full potential with the current CPU, especially in more CPU-bound games like most open world games.
You won't get the Full Performance that you wish.

I would suggest going for a GTX 1060 6GB model instead.This would bottleneck less.

Otherwise,go for the 1070 and plan on upgrading your CPU.
 
Getting an i5 8500 would requite a motherboard upgrade too.

I would also say it's better to get a GTX 1060 with the i3.

Get the GTX 1070 if you plan to upgrade to a good i5 at some time and be aware that you won't be able to utilize the GTX 1070 full potential with the current CPU, especially in more CPU-bound games like most open world games.
 
Solution