Blouch 1.5XTR seems like the best option of those. It will be big enough to max out your fuel system on E85, so going to one of the other (bigger) options you listed will just be increased lag and no more power (unless you redo your fuel). I have a very similar setup except with a Blouch 20G XTR (slightly smaller than the Dom1.5). It did 460+ WHP and 490+ WTQ on MAP's Dynojet with stock headers and stock catback. I have since added EL headers and single exit can exhaust so I'd expect it to do a little more. It would do 400-something on RS Motors Mustang dyno.