Well I think that hefty and shrock ones are the weight of an extra dude in your rig, so instead of always carrying 2 people youre now carrying 3, and in your soon to be case mac you'll be carrying 4 and in my case its like carrying 5 dogs instead of 2 and my wife and myself, so i think will a full rig it would make a differnce. but if its just you, you probably wouldn't notice.
Hard to say unless someone did a study,
Perhaps I could get a grant for a study on this, for anyone who would like to sponsor this study feel free to pm me you, your self will end up with a set of slightly used hefty skids, as i will keep the arb ones. I will need $1200 plus the cost of shipping twice. I will foot the cost of gas, the cost of shipping twice will cover the hefty skids shipped to you. Each set of skids will be taken on a 400 mile highway trip, and we will gather then data for MPG of Hefty Skids vs. ARB Skids.
HAHA
In my dreams right, but hey its worth a try.