I think it's safe enough to say that the best cycle life from any cell of any chemisty is obtained by conservative c rates and conservative depth of discharge.
A LOT depends on how those bikes are ridden. Bet the Doc's family rides less agressive than the Doc does. You can easily ride all day at 30 amps, 2c, or even less. Only pulling all 40 up a hill of about 15%.
In the Death Race two years ago, I ran this pingbattery hard as hell on 30 amp controller. 13 2c amp spikes per mile for 12 laps had that thing sagging like crazy, even though it was only half discharged. That night, it needed a huge amount of balancing time to fully charge. At the time the battery was nearly new, with about 20 cycles on it. It did not like those frequent 2c spikes. In normal street riding, you'd have a lot less of the 2c rate discharges, and more time for the battery to recover between them.
But when I recomend stuff to strangers, I make the assumption that you will ride agressive, and climb 15% grade hills 5 miles long.
I'm recomending ping to commuters, who want economy and long service life. You may notice I recomend A123's or lipo to hot rodders.
THE LIPO RULES. NEVER ABOVE 4.3V NEVER BELOW 2.7V DON'T PUNCTURE
Ideal charging /discharging range for Lipo, 3.65v minimum 4.1v maximum
See battery technology section, FAQ thread at the top of the page for lipo noob info.