I would go with a 48 in the drivers side,and a 47 in the pass side.It is what I have been using for years,and it works great.It will ride stiffer than than what you have now,but it is worth it for the better handling both with and without the plow.I would still recommend Timbrens if you don't already have them.
My stock springs were 039\046,and i gained only about an inch of lift with the plow off.They aren't any longer,to add lift,they just carry the weight better.