I just spoke with Rohana, they said offset may affect concavity from some manufactures but not with their wheels. For their wheels concavity is determined by the width. So in other words a 20x10 +25 and a 20x10 +45 will have the same concavity. However, I also found out Rohana only offers the RC7 in 20x10 +25 and 20x10 +45.
If I were to go with the 20x10 +45 wheels I am afraid the wheels will not be flush with the wheel wells and will have the tucked in look like the OEM wheels. Granted the wheels will be 2 inches wider than the stock wheels. Anybody know how a 20x10 +45 wheels would fit or look? I would like to try and avoid running spacers.