An average of less than 10 is usually considered acceptable (at least by people who author SVCDs, who usually accept less than perfect quality anyway). Most pro hollywood DVDs have an average ranging between 2 and 8, and usually a max of not more than 10. The Q level on all 3 of the discs I made now is about 2-3 average, 5 max. This means that it is LESS COMPRESSED than most high-quality professional DVDs. Consider extreme examples of compression difficulty... on one hand you could have a "video" comprised of a static black background and nothing else for 5 minutes, and on the other hand you could have a white-noise video. It might take over 15 megabits per second to get anything resembling white noise on a DVD in mpeg2, but the static black background will be "perfect" with very very little bitrate. Because of the softness of the LD source, and the noise reduction i've applied (I used a slightly different method this time around, so the "Grainy" clouds on Cloud City in ESB no longer look as such. This was actually a side effect of too much noise reduction rather than "not enough) keeps the bitrate required to maintain near-uncompressed quality VERY low. So, with "just" 3,000 kbits per second, its less compressed than some movies that require 5000 or 6000 kbits per second to appear acceptable.
If you take the original TR47 set as proof that I can be trusted on matters of video quality, believe me when I say that "quality gain" by going dual layer or using DD audio is, for all intents and purposes, ZILCH. Nonetheless, it costs me nothing to leave a higher bitrate version on my hard drive, so I did encode a dual-layer friendly version, but mostly just to keep around to show people that the difference just isn't there.