Dave...I don't think it is the E rating determining your capacity. You need to look at the tire load carrying numbers. In a 245/17 size, with narrow wheels, not a lot of options.
While you may find a few tires in 17", with a bit more capacity, than OEM, you would find many options by moving to 18" wheels/tires.
In my area, most dealers, when ordering for their sales lot, order with 18" similar tires and wheels on the 250s, as on the 350s.
One thing to consider with your 6.2 gas, is the larger, more capable, tires/wheels, will reduce the advantage of your 4.30 gears.
Jerry