I see no point to dosing gear that high. I have made test e as high as 450mg/ml, tren a as high as 150mg/ml, and a bunch of other shit. What I have learned is that dosing at a normal concentration is easier to get into solution and a lot smoother to inject. I'd rather shoot 750mg of test e in a 3ml shot and be able to walk the next day.
To answer your question about recipe, I would assume that if you did something like 2% BA, 20% BB, and all EO you could get it dosed in the 300-350mg/ml range.