I've used T400 and that had enough solvents in it that it was hard to walk or sit down for a few days after injections. Since then I've had a different view of highly concentrated gear.
From an old Cy Wilson artice:
In general, the longer the carbon chain of the ester, the more lipophilic (fat loving) the androgen molecule is and thus the more you can dissolve in the oil (solvent) without the use of a co-solvent (e.g., benzyl alcohol, benzyl benzoate).
In order to achieve the same concentration with shorter carbon chain esters as you would with a longer carbon chain ester, you'd need substantially more co-solvent. The problem is that the typical co-solvents we use can cause hypersensitivity reactions (nausea, vomiting, headaches, inflammation at the injection site) as well as irritation and even necrosis (tissue death) if high enough concentrations are used