dont use minergate own software to mine with gpu. it just not optimized. i am using a gtx 1070 as well. i am using ethminer-0.9.41-genoil-1.1.6-pre and it gives me arround 25 MH/s stock mode and 31.1 MS/s overclocked. i am using a minergate pool. search on downloads tab on alternative miners section way down., i hope it helps.

ps. sorry if i misspelled some words. English is not my native language