Do the testing yourself. I tend to notice degradation @128K and sometimes 192K when compared to their original source, usually CDs, so I have a preference for 320K but that's just me, your hearing/perception may differ. Do the A/B test yourself and see if it matters and select the next highest bit rate from where you notice the degradation. However, I will say that given the declining cost of data storage these days and the ease of transferring files from device to device I don't see the purpose for high compression codecs and lo-res bit rates any more. Back when a 20G hard drive cost $100 it made sense, now that a terrabyte can be had for around $100, not so much.