The only real advantage of buying 16x media is slightly improved faster burning times, and as dyes have matured since the days of 8x DVD-R's (Roughly from 2003, but I've to be proven wrong...)
However, crap dyes have become more common place and nobody, espically using tempremental media, EVER burns at 16x results - Not unless you want to see skipping and freezing galore
Agreed with chef it is marketing bollox, because dyes and burners are not good enough to actually handle 16x reliably. That doesn't mean there isn't a fair share of lousy 8x media. If you want to save a few bob, by all means go for 8x - But understandably burning, and verifying - will be slower.
I always ALWAYS burn at 4x, regardless of optimum burning speed on my Pioneer burner. 8x if I'm getting problems, but never ever exceeding that.
If in doubt, keep the media out.