The specs for the GTX960 are speculative. It should be a little better at least and use less power, but....
The i7 4790 is about 16% faster and you can notice the difference.
If you buy all the bits from the store, they often charge very reasonable prices to assemble them. Even if you buy the bits mostly elsewhere, you can pay to have it assembled. Perhaps that is a better choice?
Alternatively, get a good CPU and no GPU, but with a motherboard that will take one, and add your own GPU. You will need to check that the PSU will handle the load and has the connectors.
The trouble with pre-built gamers is that most of them cut corners with the PSU and I don't like that.