The breaker is there to protect the wiring int he walls, and not he equipement attached to it. Length of run is important, but a rule of thumb is 6 awg for 50 amp, 8 for 40. If you put a 50 amp receptacle on the wall run the apropriate cable and breaker. The same thing goes for 40 and 30. If you ever sell your house/shop you will most likely have bigger things to worry about than to cap off the receptacle, and someone is likely to plug a dryer into an outlet wired by a 10 awg cable. Thats when lawyers get involved.

Oh and if you're in Chicago, the code is crazy, so hire someone. Residential in that area requires conduit. They're a little extreme, becasue of the union influence and the fact the entire city has allready burned to the ground once.