I won't put any higher than 20% VG in slim ecig cartomizers. VG is thick. Your method of vaping will somewhat determine which ratios you can expect to work well. If a juice doesn't flow fast enough to wick to the coil and keep it damp you will get burnt taste, can singe cartos, damage attys, etc.
Normal Atomizer - any PG/VG as long as it flows at least as fast as you vape it
Plain stuffing cartos - I think 20% or less VG works best to get quality reuse out of cartos
Dual coil cartos (for BIG batteries only 450mah+) - some say they can use 100% VG
Reservoir cartos and tanks - like the thickness of 20-30% VG, work with thinner but may be more prone to leaking, may work with some thinner 50/50 juices