Hi Chris, welcome to the forum, and be assured that you are a mere youngster to many of us, 71 years in my case.
The Forza is about as powerful as e-bikes get, peaking at near 700 watts of power, that's almost one horsepower. Most e-bikes peak around 400 watts, so the Forza is a good choice for a hub motor bike.
However, you will need to make a reasonable contribution to handle an 18% or 20% hill, since these are electric assist and not autocycles. That won't mean an impossible effort if you are just moderately fit, but if very unfit, you might struggle a bit.
It does have throttle control, so if you hit an odd very steep bit that you feel the need to walk up, you can walk easily alongside and use the left hand twistgrip throttle for the bike to take it's own weight up the hill. This makes things very different from the old days of hard work pushing the bike as well. You can rotate the handlebar extension up so that a sit upright position is possible for someone with good reach, which your 6 foot should provide ok.
In theory it's better for steep hills to have a bike with a motor that drives through the chain and gears, so that a change down is possible as in a car. They are as rare as hen's teeth these days, the lowest price example being the Gazelle Easy rider at about £1450. However, it uses the not very powerful Panasonic motor system (390 watts max) and has a 1/1 system. In other words, you have to equal what the motor puts in, and in any event, climbing is very slow on steep hills. That said, given enough time it will climb just about anything.
The only other really powerful bike that can climb steep stuff is the Powabyke, but that's a very heavy bike, not in the same class as the others and is still a bit less capable than the Forza and also nothing like as fast.
Hope that's some help to you.
I'm also in a hilly area with up to 20% not uncommon, the odd 22.5% and even a tiny stretch of 33%. I have a drive through gears bike with the Panasonic system and also two hub motor bikes and prefer the latter pair as they climb what they can much faster than the first. Neither of them is as powerful as the Forza, but I'm more like 70 kilos and quite fit, so I still get up the hills ok.
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