Great to hear positive feedback from Vader experts. My skills are beginner, and I was afraid of messing things up, even with just this simple mod. Glad to get validation I did OK. I'm liking how it looks now, and I'm definitely leaving it alone!
Here's another comparison from the popular "You have failed me for the last time..." screenshot:

And an animated GIF of the two blending together:
https://drive.google.com/file/d/0B13YyeojRHKec0FIN01UaFFSR1lHdEtKQ3BXRnNPMEhDLVlF/edit?usp=sharingThe helmet matches movie screencaps pretty well (though it takes a while to get the camera angle and distance correct to reasonably match). I like the animated GIF view to make it easier to identify the shape features which differ. From them I've noticed the DP DLX has a bit more dome flare compared to ESB Hero, and the widows peak is sanded down more. The DP DLX eyes are not quite as arched as the ESB Hero (or the brow may be painted/shaded differently). The chin vent looks flatter and wider on the ESB Hero. The chin vent is either cut out differently or something about how the DP DLX was pulled or how it settled caused the lower part of the mask to be more vertical than it should have been. There are additional differences including obviously the reversed paint scheme. Fun to see in the animated GIF the gunmetal gray moving from one cheek to the other.
While Don Post sanded down and soften many of the minute details, I'm pleasantly surprised that the overall shape and proportions seem to be pretty accurate. The anecdotes of its undersized dome were greatly exaggerated! Correcting the dome placement and pulling back the camera to an appropriate distance to address perspective distortion makes all the difference.