Griz, I think by now we've confused you with a lot of new jargon and abbreviations.
6-8% grade is quite easy for 26" wheel bikes with a typical 500-1000w kit when run on a 48v battery. As I said earlier, if you pedal briskly, and keep the bike moving at 15 mph, the typical motor kit can do miles of 10% grade with no problems.
15% grade for very long will overheat a motor, but if you have only short sections that steep, say just a few hundred feet long, you can pedal hard, and get up them ok.
If you have longer, really steep stuff to get up, or you will go up and down steep stuff over and over like some dirt trails do, then you will need the best motor for hills. But if you have 8% hills to climb, an ordinary 500-1000w motor kit that runs 25-30 mph when run at 48v will be fine.
Those best motors for hills, in my opinion, are the slower windings, whether they are direct drive motors, or motors with planetary gear reduction inside. They are slower in top speed, but climb hills with less tendency to overheat. 20 mph fast enough for me.
9 continent and crystalyte are direct drive motors. Mac and BMC are gearmotors. Neither do any shifting, but the gearmotors have an internal freewheel that can break. DD motors have no breakable internal parts, but have the same breakable electronic parts inside as a gearmotor.
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.