License Grades

Howdy!

I've just relocated from the UK to Longmont, CO. As CO doesn't have a state contractor's license, it appears that the best way forward will be for me to sit an ICC exam. Unfortunately, I'm not very familiar with the various license grades. I've read through some of the threads here, and it sounds like there are some very knowledgeable folk! I will be doing residential work.

Since I will have to undergo the entire certification/licensing process, does it make sense for me to sit for an A certification? Or is the test so much more difficult than a B that it doesn't make sense for me to take it, being that I will only be doing residential work? How much will a B limit me in terms of the scope of my work? (I have not been able to find a definitive answer on what limits a B cert/license would have, ranging from being able to work only on residential buildings 3 stories or less, to the ability to work on any residential building.) Is it true that with an A certification, I will potentially be able to get any license from A on down from whichever city I apply to?

Any and all clarification you gentlemen can give me about ICC certification grades/testing would be much appreciated!