If you are good with business and marketing yourself, can manage several midlevels and ancillaries, and offer certain extra services, even 500k can be surpassed. It's really all about what you want out of your practice and how hard you're willing to work. Hell, build a big enough practice and you'll end up with hospital groups shopping to buy you, and then you can close out with a nice seven figure deal if you get tired of all the hard work.
http://medicaleconomics.modernmedic...iring-physician-assistant-or-nurse-practition
The economics of managing midlevels are highly in your favor- each one can boost your practice income substantially, but they require you to have a large enough practice to make them worthwhile, which takes time to build. And this neglects the income that can be made from certain gravy services that people sometimes offer (everything from Botox to laser hair removal to physical therapy and the like), which can often be performed by less expensive ancillary staff and can net very healthy profits if you market yourself well.
I actually don't see a lot of pay complaints on SDN in regard to primary care, it's more of a general thought of "if you paid more, primary care wouldn't have so much of a crisis." More demand would crop up, more residencies would open (as FM residencies are a bit easier to build and expand than many subspecialties), prestige would increase, etc.