Hi, and welcome to the forum.
Most 4x media for the 812S can only be written at 4x with the official LiteOn firmwares. I think that there many be only 1 or 2 exceptions. However, most people who want to burn 8x on 4x media do not use the official LiteOn firmware. It is possible to patch the official LiteOn firmware to allow 8x burning on 4x media. This is most commonly done (and with generally very good results) on media with the RICOHJPNR01 code (in fact, the 811S official firmwares allowed 8x on RICOHJPNR01, but the 812S official firmwares do not). See my sig for a link to how to patch your firmware for this.
For the long list of brands that have been known to use this Ricoh media code, go here: