Digging up a slightly old thread, but i recently acquired a CD32 and have been burning various discs for it... I've found that burning at either slowest or fastest speeds doesn't really make a difference as my CD32 will read them all with no problems. I've been using the same cheap brand of CD-R's for ages now as they've never let me down (700MB Datasafe - manufactured by CMC Magnetics).
... I usually burn at half the speed advertised to be on the safe side (especially if the discs contain CD audio)