A 10-weight is too much rod for steelhead. When you move from a 6-weight to an 8-weight, you may not even notice that much difference in the way the rod handles, as far as casting and fatigue go. But the step up to a 10-weight seems to cross some kind of line into "big game" territory. They are a lot heavier and stiffer, and much more work to cast. Steelheading is all freakin' day long of double-haul, double-haul, double-houl, cast, mend, swing, take two steps and start all over again. Tom McGuane said it helps to have a strong arm and a room-temperature IQ. A couple hours of that with a 10-weight and I'd be ready for traction. And it's just not necessary for the fish you'll catch or the flies you'll need to throw. Your instinct for the 8-weight is right on.
A 10-weight could come in handy if you plan on getting really into saltwater. The 8 will handle all the coho, pink, chum, or rockfish duties, but if you wanted to get serious about trying to catch chinook and/or lingcod, you'd need a 10 to handle the fish and cast the heavy flies and lines you'll need to reach and hook them. If you found some really big chum, you could probably justify a 10. And of course if you ever wanted to go to Baja or a similar location, you would absolutely need a 10 for dorado, tuna, roosterfish, etc, and bigger rods if you wanted get jiggy with wahoo or billfish.
A rod builder in Toppenish told me that the biggest rod he's made was a 10 Wt. The customer didn't want it for steelhead, billfish, or giant tarpon. He was going for shad on the Columbia. Can you believe it?