I've two of 2s 5300mah 30c ace lipos and I love them except hardcase. On a hot day race lipos puffed a little but after cooling down the cells went back to their previous form but the case didn't. I tought allways hardcase lipos are more suitable for offroad use but I'm not sure anymore.
BTW where did you find 4s Ace lipos? They are very hard to find..