For bench rest you want to have a stock that is the maximum allowed width (3 inches) on the front part of the stock for best stability. An alternative is to have a rail underneath the stock, or some other way of attaching a 3" plate to give said stability. I've used both and, at least with my shooting ability, I can't tell the difference. Although the wisdom of the sport says that the stocks with the built in width are more stable/accurate than a stock with a plate attached.
Chas