Higher dosages can be achieve by using EO as a carrier oil so yes high dosed gear is highly possible but be careful as some people get a reaction from EO. The main problem with high dosed gear is that depending on compounds the ratio of raws to solvent is an issue. Take t400 and t500 for instance, you looking at t400 being about 40% raws and t500 approaching 60% raws.. And people wonder why it hurts when you inject it...lol
Thats not to say you can't get 600mg blends such as test/eq. test/deca test/tren because it also comes down to weight and soluability of the compounds being used. But anything straight test blends over 500mgs I would be very wary