A small desk heater is usually rated around 1500 watts.
Dishwasher- 3000+
Dryer- 4000+
Oven- 2000+
Fuck, I think an Xbox 360 is rated somewhere between 150-200 when the disc drive and everything is running. Most computers are over 300 easily.
If you are worried about it, just compensate by keeping the rest of the house 5 degrees cooler or something. How do you know the dude/chick living next to you isn't running a couple 1500 watt personal heaters in bedrooms 12_ hours a day? That right there would be 3000 watts a day, which could easily run up the power bill by over a 100 bucks a month just with those two little heaters, if they were running constantly. We are going to replace windows in this house next year, but I know the heater my wife runs in here craft room goes non-stop to keep up with the freezing winter temps.
I'd go 600 and not worry about it. I would, however, keep things tight and clean incase you get a 24 hour inspection notice to give you time to bag it up and move it for a day. Then just put some stupid little heater in a bedroom and if the power bill is of concern, there is your answer.