Gotta get a heck of a thermostat for that one then. I forget what our radiator is rated at, but its just a little guy and well within the power rating for our Herpstats. For a small room, you don't really need anything massive. Just keep it sealed up and you're all set. I wouldn't risk running something high wattage on a thermostat not designed for it. Too many problems can arise from that.
We have probes placed all over our room. Most are on our racks and stuff. You just gotta average everything out and find a setting that gets as close to your desired temperature as possible. There will obviously be a little thermal gradient, but you can't really avoid that. It isn't an exact science.