said by whizkid3:I could NOT have said this better myself.
Over the phone? Taking someone's word for it based on a brief phone conversation, is not very wise.
As said by nunya, you MUST have an engineer, electrician (or qualified architect) perform load calculations. Since you will pay for this, make sure you tell them you want a copy of the calculations. Then you can post it here for us to check if you like. Considering that you have the money to build a brand new 4900 square foot home, then I am sure that would not be a problem. Likewise, I am sure you could get a copy of the plans before you spend a million $ plus. These should include the full electrical plans with load calculations. I know if I had the money to lay out to build a MacMansion (or really, a mansion in this case), I probably would not worry so much whether I needed a 400A service or not, and leave that to the professionals I hired.
Based on the size of the home, you will at least need a 200A service, that is for sure. And with 4900 square feet and some of the apliances you listed, they are likely right that you do need a 400A service. So, what is the problem? Are you planning on running the electrical yourself? If you don't know how to do the feeder calculations (not to mention the required load calculations) I suggest you step back and hire a professional. Since you are interested, take a look at table 310.15.(B)(6), which shows that the minimum is 400 kcmil copper wire for the service