The -R media code table is a bit strange. My test media was TYG01, listed in cdspeed as 4x. When changing the next higher speed id byte obviously used for 8x burning, the speed changed from 4x to 2.4x-8x, which does not really make any sense.
Anyway, simply trying to set some speed id bytes to enable a speed that is probably not implemented in the firmware was nothing I wanted to try, so I have disabled this kind of speed changes. You can however change the write strategy to any media that allows slower burning. RitekG05 allows 2.4-8x burning, so you might try this strategy change.