yes, the better color rendition is achieved with a higher sodium vapor pressure which results in more absorption of yellow light inside the larger burner.
That's a very nice lamp you have here Dave, the burner really dwarfs the amalgam reservoir!
That's indeed correct - a higher burner temperature is needed to reach the higher sodium pressure, and this causes a faster chemical reaction between sodium and the PCA vessel which, in turn, results in a faster increase of the lamp voltage over time.
I heard these lamps can cause early ballast failure as a result of the higher operating voltage. I have only once seen these lamps used in a streetlighting installation (California) but didn't get a picture of it.
Can you show it lit next to a normal 400W HPS? (if you have 2 ballasts I mean)
That's a very nice lamp you have here Dave, the burner really dwarfs the amalgam reservoir!