I use the manufacturers weight gradations as a starting point to then custom fashion my rig for specific conditions. Ive recently been using some SA steelhead # 8 on a fast action T&T 10 foot and found I could fire some bomber distances compared to the # 7 line I spooled last season,however once I started using heavy or long sink tips with larger or heavy dressed spey flies it was difficult to haul all this weight up and out properly .Once I shortened my leaders(and sink tips) used sparsely dressed flies ,my timing and distance was manageable .If your rod is a fast action you will find the upsizeing no problem in some circumstances.Some older ...slower action rods once fully loaded with the heavier upsized line do not have the power then to fire well.