I took my large front bar off years ago due to the weight, thought for sure it was 1.375", I know it flattened the car along with the old ATR 1.375 rear bar.
The 36MM hollow bar doe work better then the stocker, being hollow detracts way less than you wouls think at first blush the resistance to twist is torsional, so the diameter has much more to do with it than being solid, had this discussion with a REAL M.E. at work, we ran it thru Pro-E to compare, he proved it to me.
Pretty obvious GM figured it out too, my car does not have terrible body roll with the big rear bar and no front bar, but I will not push a car with skinnies thru a corner....