Hi d8vehI put a Q85 in a Brompton. It could climb a 14% hill with a 100kg on board without pedalling. That was at 36v and 14 amps.
A Q128 at 48v and 20A should manage 28% with the same bike and rider.
A Xiongda at 48v and 15A can easily manage 30% hills with a 100kg rider and 26" wheels.
Generally, hub-motors can produce more power than crank-drives, but to get them to climb, they need to spin at a reasonable speed, which means that you need one with either a high internal reduction ratio or a small wheel or both. One with a low winding speed will be more efficient when climbing, which means greater efficiency and less heat.
Can you recommend where to buy above wheels and controllers? I'm struggling to find UK suppliers of these items. And will all controllers work with all wheels, and will connectors need changing? It's all very confusing.