Welcome to the party, Digger! I have a model 1, and don't have any problem getting up to the 250 temp. You might want to contact Steve for a little tech support. As far as adding the bigger element, I believe you'll be limited by internal dimensions (they're longer). The #1 is 13 1/2" deep, the #2 is 15", and the #3 is 20". You'd have to ask the experts out there, but I believe the higher wattage of the elements is needed simple due to size (more element to heat).
When all else fails, call customer support! They really are great people, and will steer you right.