The words heft and hollow don't really go that well together :<0) I would say use the size your most used to. It just seems to me that if your trying to compare, the less variables the better. If your not used to using a 7/8 that just may add to your discomfort. My rotation consists of 5/8 to 8/8 all very hollow and while there is a small difference in weight, the width and toe shapes make more of a difference to me. That's just my take on it. Another way is heads = 6/8, tails = 7/8. Call it in the air