I just spent the last 20 minutes writing and trying to explain why you can't compare steelhead to saltwater fly fishing. I gave up and deleted it all.
In the 70's when I first started saltwater flyfishing, and still living in Oregon, I would ask the same questions, and got very few answers.
Let me ask a question, how many hours has it taken you to catch the steelhead you have landed? .....So standing on the deck of a flatsboat all day for a shot at jumping a giant tarpon does not sound so bad does it?
Fighting a hot 20lb Dean River steelhead may take me a half hour, that's 40 lbs an hour! A 125 lb tarpon may take me an hour, that's 125 lbs per hour, right?
Can you compare? I don't think so.
You can use your steelhead rods, other than spey, for snook, redfish, bonefish, permit and yes baby tarpon, but that's as far as it goes, they're really just tools used in a different way in saltwater.
If you are wondering about equipment, any good fly fishing guide has good fly fishing gear.
I'm a saltwater guide who grew up steelhead fly fishing, and I will share all of my knowledge about either, and if I didn't answere your questions just ask again.