Should I upgrade my CPU or GPU?

Hello,


My wish would be to upgrade one PC part (CPU or GPU). I use it mainly for gaming. So I would like to run new games on high settings. I have:

CPU: Intel Core i5-4440 Haswell Quad-Core 3.1 GHz (3.3 GHz Turbo) LGA 1150

GPU: Gigabyte GTX 770 GDDR5-2GB

as far as the performance goes, there dosn't seem to be a major bottleneck, usually GPU usage is 90-99% and CPU usage is ~80-95%

I have no problem running old games on high settings. But with the new ones, I have noticed that a upgrade may be required to achieve the results I want. So when checking the game requirements from: http://www.systemrequirementslab.com/cyri . My PC always passes the minimum requirements, but as far as the recommended requirements go, most of the time it wont pass, because some part needs to be upgraded, and most of the time it is my CPU, rare cases GPU(because of the Dedicated Video RAM).

So my question is... which part should I upgrade: CPU or GPU?
Many people say that it is smarter to upgrade GPU. Because upgrading CPU (going for i7). i5 vs i7 won't make a huge difference, when it comes to gaming?

So would it be smart move to go for i7 and retain GTX770? Or should I retain i5 4440 and go for ex. GTX 970(would it be worth the money)? Most certanly GTX980 would be worth the money, but it's pretty expensive....


Thank you in advance,

Chris