Using a 60qt Aluminum kettle, I can take 5 gal. of water from 60*F to 168*F in about 30 minutes.
My only reference kettles to compare against are a 30qt Stainless Steel or another 60qt Aluminum.
But I owned a S/S Keggle for a brief period of time and felt that it took much longer to heat than my other kettles did. No real data, just "felt slow to heat".