Over at the LG forum they have numerous posting with 16X media burned at less than 4.30 minutes. A very fast drive.
But I agree. There is nothing wrong with your Pioneer. It will do better with -R media, and a lot of people would argue with me if I tried to assert that my LG is a better drive than the 109. There is a lot more to quality than speed and any drive will take a little looking to find a compatible 16X media. I recall that there are some media that are not so good with LG either.