Agree w/ above, and remember that private practice earning will vary depending on the business savvy of the MD. I think that gets particularly hairy w/ mid-sized groups, who are large enough to need staff and square footage, but maybe are spending more on things like space and staff less out of need and more out of want. A smart young grad could do quite well if willing to take call and other less preferred work away from some of the more established folks.
Working as an employee is also highly variable based on the market you are shopping in, how many patients you are willing/able to see in the amount of time the clinic is open, and whether you are in or outpatient. Most importantly, perhaps, the benefits/bonus packages are highly variable.
I had an interesting conversation recently w/ a specialist who contracts w/ government agencies (CHCs, detention centers, etc) and does very well. He observed that most contracts are written and negotiated by corporate types, and by showing up himself, he cuts out the middle man and is able to negotiate his own terms. I was trying to decide how a family MD could do something similar.