Why don't you have a look at the scans posted in the following threads:
Post your BenQ DW1655 SL scans here
Post your BenQ DW1650 SL scans here
Then you can compare the results other people are getting with the same media.
I seriously doubt you're going to be able to find a write strategy swap that improves on the strategy already in the firmware, but you can try to experiment with SolidBurn On/Off for known media and also with WOPC Enabled/Disabled.
It's possible that your TY 8x DVD+R media will burn as well at 12x as they do at 8x, but that's not guaranteed so you may have to burn these media at their rated speed for best results. If you're using TY 16x rated media, they will probably burn equally well at 8x, 12x and 16x, but you can test this yourself.
When you perform scans with CDSpeed, you should ignore any jitter spikes that appear at the point where the scan speed "dips". Apart from such phantom spikes, jitter should be 12% or lower, and an average jitter below 10% should certainly be achievable.