you can use anywhere for 8-12lb tippet,i prefer 10. if your using a floating line dead drifting egg patterns with a strike indicator is your best bet because a floating line wont get a swung fly down deep enough.
Here is the rig i use :
fly line:Floating line
leader: 6-9ft 10lb leader
indicator: medium or large thingamabobber set to where the flies are 4-12 inches inches off the bottom
dropper rig: one size 2-6 weighted egg pattern or marabou fly and a size 6 unweighted egg pattern 12-18 inches behind it
I have hooked a few with this but still have not landed one.
and a 6wt is quite a bit on the lightweight side FYI 7-9wt would work better for you, that is winter steelhead of course, summers a 6-8lb leader and a 6wt would do fine. 3 reasons i suggest a heavier rod for winter steelhead.
1. faster/higher water. in winter the rivers are a lot higher and fast and a heavier rod is a must to handle a fish in heavy current at times
2 weight. heavy flies and strike indicators can be tough to toss with a lighter rod like that and can make fishing very difficult and tiring
3. the fish. winter steelhead average way larger the summers and are often over 15lbs. fighting a fish that big with a 6wt can result in a broken rod rod or lactic acid build up in the fish killing the fish.
just suggestions not telling you you can't fish your 6wt for winters or anything

. if you ever want to try fly fishing for winters send me a pm, i could show some stuff if you don't mind heading north a little ways. forgot to add a list of flies i have had success hooking fish with.
egg patterns:
lowly glowly size 4,6 orange
volcano egg,size 6 pink
glo bug size 6,pink,peach
bead head lifter size 6,pink
veiled egg size 6 pink
leeches/wet flies:
pink moal leech
you can order these at caddisflyshop.com
or go to their shop in Eugene and ask about winter steelhead nymphing and they should set you up.
EDIT: i forgot one important factor, rod length. it is important to have a long enough rod to achieve a dead drift presentation by either mending your line or high sticking it. High sticking is when you hold your rod high and follow your indicator through the drift keeping your fly line off the water but you leader and indicator are still dead drifting, this is easier on smaller streams or when you are not too far away from the water you are targeting, but this is where the rod length comes in. with a longer rod you can high stick nymph at longer distances and can mend/manage your line easier for a better presentation. i use a 9ft rod (shortest you want to go) it works for smaller streams but can even be a bit short on those. 10ft rod is the perfect size for indicator fishing for steel,7-9wt.
brandon