You don't have to go to MP3 at all with your submission. Your can literally mail an Audio CD or burn your full-quality uncompressed WAV or AIFF files in a Data CD and mail it in.
I can easily convert to MP3 at the latest possible stage of production -- currently, I do not know for sure how many total minutes of music we will get in submissions, so there is a chance that we may be able to produce Audio CD's instead of MP3 CD's. In the odd chance that we can go with Audio CD's, compressing your material now would be a waste.
So the basic strategy is to preserve full audio quality until the very last possible moment, and then only do lossy conversion to MP3 as a last resort to make everything fit in a TWO DISC set.
I can understand if some one who use amateur recording equipment recorded something that wouldn't sound any better regardless of whether they encode it with uncompressed WAV/AIFF or at compressed 120 kb/s MP3 -- in that case, there is no reason to take up addition MBytes because you'll not gain any perceptible audio quality with the additional MBytes.
For those with professional grade recording gear though, I'd suggest you retain full audio quality all the way until the very last moment -- until we're absolutely sure we cannot fit your material without compression -- then we'll convert (and will choose the highest possible bit rate that would fit).
Of course, that's not to say that you cannot also make a separate, aggressively MP3-compressed version of your recording for the sole purpose of uploading/posting to Piano World so people who don't buy the CD can download that one from the Piano World website. The version on Piano World website can (and probably should) be more aggressively compressed than the version we eventually put on CD -- the reason is simple: we can put way more MBytes of audio quality on CD than most folks can download over the net (not to mention Frank having to pay for Piano World's download bandwidth usage if every one starts to download CD-quality music at 10 MBytes/minute, versus 1 MBytes/minute if the same material is compressed to 128 kb/s MP3).
I hope this makes sense.