Bottleneck is a very relative term. Here's how I will put it: the i3 and the 1070 is not a good pairing. There are worse pairings you could buy, but this is not a good one. For your case, I would suggest dropping the 1070 to a 1060, and replacing the i3 with the i5.
Unless of course you are buying the i3 with a future upgrade in mind. If you are planning on upping to an i5 or i7 in a few months or whatever, and are willing to deal with the i3 being a limiter, then the 1070 might not be a bad idea right now. However, I personally find it more worthwhile to get a kicking CPU first that will last you a good couple years, rather than a kicking GPU now that will be outperformed by a cheaper GPU in a year.