Yes, I understand that there are limitations based on the chipset.
I was surprised that many custom modes report "maximum bandwidth exceeded" when obviously it is not a bandwidth limitation. For example, 2560x1600 at 30 Hz was accepted, but many other lower resolution and lower Hz framerates report the bandwidth limitation error.
Additionally, the famerates available appear to be limited by the driver. I was trying to set my main display to a lower frame rate and resolution to ideally allow for more bandwidth for the external monitor, but it would not allow custom settings in many cases.