A good average quantizer aim for 1CD backup?

[MetalPhreak]

I only recently started using x264 and was just wondering about what is a good quantizer to aim for when making 1CD backups while still maintaining decent quality?
I did a movie rip the other day, encoded at 640x272 and got an average quantizer of around 20. Judging by the quality (in my eyes) I could safely bump the resolution up a bit.
It would be greatly appreciated if someone could point me in the right direction.

[bond]

why not simply specifying a bitrate?

[Caroliano]

I think that he is already doing it and seeing the resultant average quantizer.

22-30 is an good quality range. But you may can't reach this in every movie that you do because every movie compress diferently and/or have an diferent duration.

[MetalPhreak]

But you may can't reach this in every movie that you do because every movie compress diferently and/or have an diferent duration.

Yes, I'm aware of that. I just wanted something to aim at to get me started, but you also answered this so - Thanks.
I'm just new to x264 and it's a bit slow to test X amount of settings.

[stax76]

Making a prediction what quant is needed might be possible with the help of a compressibility check. I don't know if anybody is doing this using x264 so I can't share experience with it.