Since you already have everything lossless, it doesn't really make much difference. I would do them at 128 or 160, and then re-do any at a higher bitrate if you can hear artifacts on those tracks ...

I need to come up with a process to help my dad (and me) maintain his music library (~10k songs right now, all ripped from CD). Basically he needs to rip to Apple Lossless for archiving purposes and ...