either way, a 2mb buffer is fine, even @ 52x. I've never had a coaster @ 52x. The media has to be able to handle the write speed before you even try a 52x burn.
As BuddhaTB said, you don't really need an 8mb buffer anymore.
I believe Yamaha & Samsung are the only companies making 8mb buffers anymore. I'm not sure about Plextor though.
Nero has the ability to set up it's own internal buffer manually or automatically. Mine is set to auto, and I've never had a problem. (33mb I believe is the current setting).