In my sporter weight rifles I generally give the barrel about 0.030" clearance which is plenty for fine accuracy and appearance as well. If the customer wants more I will give what they want but I do not like going much less.
For my heavies or extreme range rifles, I will give 1/16" clearance(0.0625").
Remember this needs to be the clearance you have in the shooting position. I increase the clearance on the heavies for the simple reason that the barrels are much heavier then other rifles and thus will flex teh stock, any stock, more.
I do not want anything touching these fine barrels so I float the entire length.
Also remember that if you are a shooter that likes to use a tight sling around your support arm. Be sure to check that this type of hold does not pull the stock forend to one side and rub the barrel or even get close to it.
While I personally feel 1/8"(0.125") of clearance is more then needed unless it is total clearance(0.0625" per side), it certainly is far better then the occasional stock-barrel rub.
Just to give you an idea, McMillan allows 0.075" per side of clearance for a total of 0.150" clearance on their heavy BR style stocks. Course these are designed for 15 lb barrels as well though.
Good Shooting!!
Kirby Allen(50)