My meter will read ec but I dont ever look at it I just use the ppm. I dont know what .5 .7 equates to for PPM. I use 1200 all the time for mid flower plus I'm only using a 400 buds dont get to dense unless it's the genetics like BOG SB those get dense all the time.
Yes strains will have differing reactions to higher ec levels. you can tell if you have a sensitive plant. My girl is taking 1200 no problems. Im using Happy frog
....this link is to an old thread of mine... a few people chimed in with their feeding schedules broken down weekly by ppm... have a look at Dr.Dog's... he's a heavy feeder and his meter is a 0.7 like yours... i might add he is also a super pro at what he does...