70/30 is better, for sure.
You can go searching, but the only time I used 50/50 liquid (Vapemunki) I needed to suck in a little juice now and again. Depends on power of course. 11w on the iStick is probably 14 watts on "normal" mods.
Maybe ask on UKV, there's possibly plenty of high(er) VG users on there...