well 42/19 would be way too much pedaling for fixed. While the "easier to pedal" ratio is perfect for single speed since you can coast once the cadence gets too high. "typical" fixed ratio would be somewhere around 48/17. that's what i run and i often find it to be too much pedaling, but i everytime i climb a hill i'm reminded why i keep it. A friend of mine says that he averages about 21mph with this ratio and maxes out at 34mph (he has a computer). obviously these aren't accurate and change from person to person, but this can give you an idea of a "common" ratio.