I did the 6x9 conversion. Wayyyy better sound and bass. I do have the premium sound upgrade and this addition made it 10x better. I used JBL club series 3ohm speakers and the highs are just right and put out great bass for a 6x9.
Also, make sure if you do the 6.5 or the 6x9 conversion that you check the polarity of the wires. Even with adapters, I found they were reversed. I had to cut the adapters and switch the wires.