There does not appear to be any limitation, outside of what you might have available as a remote user.
I would think that the maximum resolution on the MBPro screen is whatever your MBPro supports -- not controlled or limited by the desktop PC. So, if you are viewing the PC screen from your MBPro, your MBPro won't show you more than what you would see on the PC.
Can you adjust the PC's video settings while viewing/controlling the PC from your MBPro? If you can, what is the highest setting that you can set from the MBPro on your Windows PC? There's your answer - if I understand your question correctly.