I think it depends a lot on when and where. On my commute in the suburbs it virtually never happens that I am moving faster than traffic. The only places are the railroad crossing (cars are stopped) and a four-way stop on my commute (too much traffic for a stop sign, ought to be a street light. So it backs up for quite a ways with cars slowly inching forward).

At the four-way I don't split lanes, though I could. when I was turning left there I would ride up the left shoulder AFTER it widens out (there's a left turn lane that is currently hashed off, whenever they put a light in the intersection it'll be a left turn lane), and now that I am going straight there I'll get on the sidewalk and ride up to the light, but I don't split lanes or ride up the right. There's no right shoulder, just a curb, so all it takes is a car a little over to the right and I couldn't get past, and if I split lanes I'd wind up at a stop sign with a car on either side about to take off which seems like a bad situation to be in.

I have split lanes at the train intersection but in that case there are no cars moving at all. (I've also ridden under the train gate and across the tracks... only while the train was receding however never when it was approaching).