I just looked at the specs for a Suburban 6 gallon water heater.
10.3 GPH on gas, 6.1 GPH on electric, 16.4 GPH with both. So, gas is about 1.5 times faster than gas. So, in theory, if you use less than 16 gallons of hot water per hour (about 0.25 GPM) using both gas and electric, you would never run out of hot water.
Rick & Debbie; Brandy, Dexter R.I.P., & Fritz R.I.P. (The Doxie "Kids")
2015 Jayco Pinnacle 36RSQS 5'er
2011 Rockwood Windjammer 3001W (Traded)
2013 Chevy Silverado 3500HD LTZ, 6.6L Diesel Dually; B&W Goose Neck and Companion 5'er hitch