Overlock GTX 1070 can increase hashrate to 510~520+ Sol/s, each card.
But it's may be unstable(crash, black screen etc.), you need to do some test, find the right settings of your card.
Overclocking memory on a GTX 1070 doesn't seem to help noticeably IF at all on equihash mining - overclock CORE does help some usually.
Might depend on the specific card though.
My Gigabyte 1070's and 1070ti's definitely benefit from both core and memory overclock. I have done extensive testing and both seem to increase hashrates independently, around 5 to 15% I only mine equihash.
I didn't say anything about 1070 ti cards here - and do keep in mind I'm the one Voskcoin credits with the "+200 +700" settings he used in that first 1070 ti equihash rig video of his. 9-)
Many of my 1070 cards ARE Gigabyte, and dropping memory from +500 (as high as they go and stay stable) to -500 had ZERO effect on hashrate.
Might be power level related, since I'm running them around 105 watts for EFFICIENT mining, not pushing them for max hashrate.
Might also be a difference between LINUX and Windows or the specific drivers, but I doubt that.
My 1070's run with a +650 mem overclock (totally stable) and reducing that to zero or even only +300 reduces hashrates noticeably. I run my cards at 65% which equates to around 120 watts. Running on Windows 10 with the latest drivers.