Apparently, the Adobe Standard Camera Profile is no longer an option in ACR 6.6. It is gone.
The ACR 4.4 is now, again, the closest match to 'very careful' custom profiles created with Xrite ColorChecker Passport software.
The continued evolution of Camera Raw's software has been an interesting ride. While being a committed fan of the Adobe Raw technology, I guess the expectation is the "Camera Standard" or default camera profile would be a closer match (not sure what the default is now). Seems the canned camera profiles (camera specific) are being relegated to a set of artistic options instead of a universal standard - or starting point.
Either way, I have found the experience with camera profiles to be a major advance in my personal photography. My custom profiles are so good that I almost can't believe working again, without them. The other side of this experience is that before the arrival of the Adobe Standard in ACR 6.x, I didn't even know that camera profile management was even needed. A wonderful ride indeed!