Ok let's do some simple math for the shaft you're looking for...
3 oz = 85,02 gramms. I've got a cf tube 30" long recently for some experimenting and its weight is 50 gramms with wall thickness 0,9 mm at the tip end and 1,25-1,3 mm at the joint end. I don't think Revo c.f. blank is significantly lighter. So 85 - 50 = 35 gramms that is how much is left for the phenolic insert at the joint end (if you want unilock insert in there add 10-11 gramms more). I guess you'd like it's filled with some foam but not the air so to feel better while shooting but in reality forget about it if your preference is 3 oz shaft...