I've pretty much got the same question as aCIDfire, so I'd like to add it in this topic.
My 3520A has original NEC 3.07 FW, which I've flashed a long time ago.
But, last week I've bought a pretty large batch of INFOME R30 +R 16x discs (Philips), because of good experience with previous Philips 8x discs. The exact same type wasn't available anymore, so I thought best way would be to go for these 16x discs.
Unfortunately they seem to give a much higher error-rate (and thus resulting in much slower reading speeds) than the previous (iirc) INFOME R20 +R 8x discs (Philips). I always burn at 4x, because my system is not too fast. Never had any troubles with the previous discs.
So, to recall aCIDfire's question: Which firmware is best for burning quality (is this mediacode-specific?), when burn speed is totally irrelevant?