Welcome:). According to this PST3 OP readout , the Verbatim +R8x (MCC 003) is rated for only 4x burn speed. I am not sure, but you may be able to use OP to check the 8x box, but there may be a reason they are only rated at 4x, so don't expect miracles.
Your drive is also rated for 24x max CD burn speed, so a fall-back to this speed may be normal. What speed options are offered for this media in your burn program?