need some advise
Ben, I hope you do realize this post is more than a year and a half old. I would assume this project is completed.
Also, yes, in the situation you describe, a 4-wire feeder, the grounds and neutrals are not bonded. In the case of a 3-wire feeder though the grounds and neutrals DO get bonded. This point needs to be clarified.
Voltage drop is not dependent on distance only, and a feeder is not calculated at full amperage. You need to know the actual load or demand load in addition to the distance to make an accurate suggestion as to wire size and voltage drop. Of course bigger is usually not any worse other than cost wise.
I see in another thread you are an electrical novice. If you insist on giving electrical advice PLEASE be very certain any advice you give is well researched and documented. A disclaimer would not be a bad thing either.
There is WAY too much erroneous advice given over the web and electrical is no place for off the cuff advice.
Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.