I'm 6'2" and 225 (and falling ). 3-5% grade is pretty much standard fare around here (Boston Mtns, in the Ozarks); the hills don't really count as hills until they are >5%, but generally, I'll range from 7-18 mph, depending on the day, the wind, and the hill. 3-5%, if continuous, can really bust a big guy's ass; 3-5% rollers are easy to hammer over.

My ride today had about 6 miles of 5-7% climbs, interspersed with 3 or 4 short downhills. I averaged about 10 mph up, and about 28 on the way down (curvy road).