I think that 6 ft-lbs would be more than enough. I looked in my owners maunal for a 2001 RM250 and there is no spec. Just as a side note the clutch bolts are torqued to only 3.5 ft-lbs. I personally go past snug about 1/2 turn with a 1/4" drive socket wrench.
The clymer service manual says for 92-96 CR 125s the intake manifold mounting bolts (ie reed cage bolts) torque spec is 9 ft-lb. It's probably the same for 250s, they don't have that torque spec listed, surprisingly.