It matters not whether the difference is significant, it is a matter of direction. It's often easier to work these things out as being case A or B by comparing an amplified version - In case A you have a 50kg rider and 40kg bike. In case B you have an 85kg rider and a 5kg bike. You then decide who has the easiest ride. If you arrive at case B in the extreme, then chances are it's going to be case B in the lesser extreme scenario. Of course, it may not always be that simple..