The biggest problem with high vg is just as said above, it will not travel through the wick quickly enough, coils will gunk up quicker and you will get more dry hits. Vg is thick, pg is thin. With that tank you probably want to stay with 70 pg 30 vg. There are ways around the dry hits to a point, like just waiting longer between puffs, or covering the air intake (which I'm not even sure you can do with that tank) and sucking on the mouthpiece without firing it to pull more juice in to the coil. You'll still go through coils faster and will get more burnt hits.
You can try different ratios of vg and pg but should probably go 50 50 or thinner (more pg).
Pg also gives more throat hit, vg is smoother.