Well, as of today I use a 2 weight for Steelhead apparently.
That said, I fish Chum and Coho on 5 weights. Ive never played a fish over the 5 minute mark (I would say 90% are 3 or less) but having a bit more backbone does help you crank it in. If I were fishing bigger flies, on larger rivers with heavy sink tips, Id want a 7 or 8 weight. But I enjoy the slower water Coho like, where I control the fly and not the current. Just my opinion, and a 5 weight is more than enough backbone for fish under 14 pounds.
As far as spey goes, dont go switch. Everyone I speak with who has switch rods says not to waste the money. They dont do spey or single hand exceptionally well. Go one or the other. And spey is an entire new game, vs single handers. By all means, go for it, but I like my single handers a lot (for now.)