I have only 1780 with gtx1070. So 2k is good!
As always, there's a good chance that SP's "2k" is with the card overclocked at 100+ TDP, consuming almost like a gtx 1080. 
And the actual gain compared to the free miner will be ~7-8%. Just like it was with keccak.I think the main thing that will hurt sp_ and his buyers of this mod is stale shares. sp_ isn't good in optimizing miner <=> pool communications.