I just ran a 6.5 preboil volume boil on a 45k burner. I had to actually turn the valve way down to keep the boil under control. I was fighting a boilover for the first 10 minutes, until I decided to back the heat off some. 30k should be fine for getting 6-6.5 gallons to boil temps.
Granted this was in a 30 qt turkey fryer pot (tall and narrow), so I'm not sure how your pot might compare.