The problem with the Ping is that it cuts out at 60 amps, which happens during peak current for the 5302 when starting up from an abrupt stop and going up steep hills. When this happens, it requires disconnecting the battery and reconnecting it, which can be inconvenient. One way to avoid this is to increase the current limit on the battery by adding solder to the battery's over-amp shunt. However, some feel uncomfortable doing this mod.
Anyways, the 408 should go about 24 mph top speed, unassisted, at 48V. If you want a higher top speed, you should look at a "lower number" 40x motor like the 405 or 404(purchasable from ebikes.ca) which should get you to 30 mph top speed, unassisted. Since you're living in a non-hilly area, a faster speed bicycle should suit you fine for what it lacks in hill-climbing power. If you want more hill-climbing power or greater acceleration, you should look at 35 amp or higher controllers with whatever 40x motor you're looking at. The higher amp limit should let you take advantage of that extra power the 48V20AH can give without causing it to cut-out.
(BTW, endless sphere is haven for this kind of information. The forum members there are... well... very helpful.
- including me.