To solve this issue, I mounted a 1500w 120v heating element in my kettle, which plugs directly into a GFCI outlet (no output control, it's always at 100%). This, combined with about 80% heat on my largest burner (which I replaced with a 2600w canning element to give extra power and support the weight of the kettle) lets me get 7.5 gallons or so to a rolling boil in under half an hour.
Fermenting: American Stout
Kegged: Biere de Garde, Premium American Lager, "May Day" Belgian Pale Ale, "Witty Retort" Light RyePA, "Spring Break" Marzen
Bottled: "Sh!tshow" Schwarzbier, Maibock, Saison, Kolsch