An i5-4460 and an i5-6600K are really pretty similar. When people say their CPU bottlenecks their GPU what they mean is that it doesn't matter if they put in a better GPU, the performance is CPU bound. For example, if one has a Pentium G3258 at stock and a GTX970 and were to say that this is CPU bottlenecked then their performance in games would be the same if they upgraded the GPU to a GTX980, 980Ti, 1070, 1080, Titan X, 980 Ti 3-way SLI. Doesn't matter, the CPU's the bottleneck here and the CPU is what's limiting the performance. Conversely people would say you shouldn't buy something that's bottlenecked - what this means is that if you have a G3258, as an example, and buy a 980Ti it's a waste of the GPU since it would perform the same as a 970. So you'd be better off buying the 970 and putting that money you save towards a better CPU, RAM, SSD, etc. Hence a G3258/980Ti build may be rethought and rebudgeted to an i5-4460/970 combination.
However an i5-4460 does not bottleneck a 1070. That's not what's happening. Honestly, if you hadn't posted that you have some other games and situations where you get >100fps I'd ask if you plugged the monitor into the motherboard instead of the GPU.
Run some benchmarks and confirm to yourself that your card is working correctly. Do all of this off-line. I'm with Chaos2Theory here - your internet connection could be choking stuff or that particular server may not be sufficient (assuming, eg, you have a good internet connection).