I've been using my summer waders for steelheading in the winter. The important key is extra rooms in the waders for winter layering. I normally have 3-4 layers underneath the waders: a mid-weight or heavy-weight base-layer (a wicked dry and non-cotton materials), 1 or 2 mid-layers (fleece pants, again non-cotton), an outer-layer (a thin wind breaker type Gore-Tex pants. This is very important, because the extra layer of Gore-Tex will guarantee to keep you dry.)
As for the boots, extra rooms and layering are the keys also. I have 2 pairs of wading boots: size 9 for summer and size 10 for winter. As for socks, the first layer consists of a thin base layer socks (absolutely non-cotton) and the second layer is a pair of thick Marina wool socks. To keep the toes from getting numb, I put air activated heat-packs in between the first layer and the second layer. Do not put the heat-packs on your skin.
This keeps me mobile and warm. 6-8 hours is a typical steelhead outing.