How much do you want 2.0, 2.5, 3.0?
No more required, I was just trying to point out that although 1.67 (60%) seems like a large margin it is in fact nothing like as large as many people think. It is eroded by not using max effort braking and often further eroded by poor technique and bad decision making to the point that an overrun occurs. Reverse should in theory give you extra margin but if used in conjunction with autobrake won't normally decrease your stopping distance.
The bottom line is that if you land on a runway at the max regulated weight you will be very unlikely to have 40% of the runway still in front of you by the time you stop.