My CD32 plays all the originals I have fine. I tried the 700MB Maxell CD-R's burnt in Nero 10 and they usually work.
The first burn of Heimdall 2 I did didn't work but I tried it again it worked fine. The 888 CD only occasionally loads and a custom WHDLoad disc I made myself loads only some games but with horrendous graphic/sound bugs. I will try burning these discs again.
The slowest I can burn is 10x but I have burned discs at 24x which have worked perfectly. Seems to be hit and miss really; If the first burn doesn't work, try another one.
By the way, the Maxell discs are a good price in Costco (UK) - £12.58 for 100!