I wouldn't use Aromasin on-cycle. It is best used in combo with Nolva for PCT. I would use Armidex instead because it is great for cutting estrogen in half. Start with .5mg/EOD and then move up to 1mg/ED if needbe. This way you aren't crushing the estrogen in you body and raising natural testosterone production needlessly like aromasin would.
Letro is the strongest AI of all, but that should only be used if the Arimidex isn't enough on-cyle. Since you are using test and dbol, you may have this problem and will need to switch to Letro. You can always use just a small dose of Letro (.5mg/ED) and it will go a long way!