yeah, imperials are hard to do in any case, but if your stove lacks power, it takes forever. My recent IIPA took 2.5 hours to boil from 8.5 gallons to 5.5 gal. Its only a 7.5 gal pot, so I added fresh wort as room become available.
Thomas had success insulating his pot for a better boil, but I'm planning to use mine with gas over the summer, and need it to fit properly on the stand.