What are the issues with the XR on the MBP screen.
There's something about white LEDs that causes inconsistent results out of the XR. I've noticed that it manifests itself in terms of different color casts from profile to profile (I have a 17" MBP with a matte screen myself, although I don't use it for editing, I do have it profiled).
Edit environment changes from inside a seaport-type case to a blackout tent with-in the day. [/quote]
If your ambient light is changing then your screen luminance should be as well. I'd recommend a different profile for each environment. If you set the display settings to "Apple Cinema Display, iMac, laptop" then CEDP will reset the brightness for you when you run the LUT Loader so...
In system prefs select the appropriate profile
Hit command spacebar (this should bring up Spotlight)... type in lut (should bring up the LUT Loader) and hit return (or you could put the LUT Loader somewhere where it's quick to get to).
Your backlight level (and thus the luminance) will automatically be adjusted.