yes, as mike just pointed out, the trail thru ventana wilderness is tough. he and i and another bpl'er did a 25 mile loop this last weekend and it was intense, to say the least. alternate sun and snow, gusty crazy winds and fog at night clearing to freezing temps in the early morning hours. we completed that yo-yo as described by "sawchuck."
the other route mentioned, the point reyes loop, is long, but the trail is clear and smooth and the intensity comes from mileage alone.
my two cents for an intense trip would be what you already mentioned--lost coast. you can do it yo-yo style in either one of the two sections. there is a redwood section-- the south section, sinkyone wilderness-- that goes thru a bunch of valley folds and has some cool beach campgrounds, like little jackass creek. (black sand beach, fresh water). the north section is all beach hiking with camps at the outlets to the streams. either of those sections could be done in a yo-yo. that is rugged, wild land but the trail is at least clear. you'd prob want to call though, b/c the trail is prone to slides, to make sure all is good before making the long drive up the 101.
theres also yolla bolly wilderness, which would have some snow up high, and/or the snowy mountain wilderness areas, which are in the coast range mountains. intense comes from the ups and downs and little water, but at this time of year, that shouldnt be a prob.
anyway, have fun and good luck!