The meaning of those 1's and 2's that indicate priority marks media that is popular or is popular AND needs fine tuning. They do not indicate a performance difference.
/HPdisable16 indicates a media that should not be oversped to 16 on some or all drives--even though the latest firmware will overspeed this media on all drives. It's my guess that if you see this mark on a media that you should not burn it at 16x because it will give choppy playback in a set-top player. Media marked this way will all burn faster at 12x, and with better results.
You will need to correlate that list with other sources of information to get any sense out of it. But, it will tell you what medias most DVD writer customers should purchase according to BenQ. However, Daxon (a "1") made by BenQ still does not outperform Infodisc (a "2"), and personally, I don't recommend either one.
A good place to start would be our media scans listings, supermediastore.com, newegg.com (reviews), and cdspeed2000.com (for CD/DVDspeed software). Oh, and Verbatim +R (MCC) medias are a great place to start. That P9 firmware you mention is a very good thing too as it has zero problems relating to computer chipsets or software.
Anyway, back to your question of that listing. Compare that with BenQ's popular overspeed listing. Ditch everything that isn't a 1 and ditch everything that isn't on both lists. Compare the remaining media codes to see if there are any phase out medias such as a 4x and 8x similar in price by the same manufacturer, and then cut the phase out, out. Next, compare the remaining media codes with data from scans on this site to cut out any bad performers. The remaining "distilled" information will tell what media to purchase for your BenQ writer--in the future. This will help you to avoid the average 10% coasters common with junk or phase-out medias. But, if you're willing to gamble that the quality hasn't changed yet, there are some nice phase-out medias on sale right now.