Yeah, you are right. It works @24x when I disable the Smartburn option in Nero. The quality is also fine. I just made a Nero CD Speed quality test and the result was 100.
However, there must be a reason why Smartburn limits the speed to 16x. Maybe the reason is that I burned the CD-RWs with my LDW-811s before. Maybe NEW CD-RWs of the same type would work @24x from the beginning on.
Furthermore, there are some DVD+RWs which I burned on my 811s and then tried to erase and burn them on my 812s. The burning process is successful but there are unrecoverable read errors on the disc. When I use a brand new disc of the same type (same brand, same media code, same batch), there is no problem at all - even after intense use (several times erasing, reburning).
So I guess you get the best results when you use brand new Rewritables on this drive.