Making an ebike more efficient for road rides

[Electric_Andy]

I think you are hoping to find a sweetspot that doesn't exist. An E-gravel bike is about as efficient as they get if you put slim road tyres on. You could plough a lot of time and money into making all these tweaks, and for very little gain. e.g I once had a hardtail MTB and found I wanted to do more road riding. I changed the tyres, altered the bars and seat, shaved off as much weight as I could. The only noticable difference was the rolling resistance of the tyres, and that's going from full on nobblies to slim jim baldies.

If you absolutely need more range then the only way to get significantly more is to get a bike with a larger battery, which of course would be heavier and not as road-focused. It's a bit like when a teen gets a 125cc and spends loads on fancy exhaust systems, premium fuel and racing engine oil...you only see about 2mph difference at the top end. Which can easily be wiped out by a slight headwind and a few pies the night before. The only real gain comes when you get a larger capacity bike

 

[N0bodyOfTheGoat]

I think the biggest factors by far are the climbs, the total weight of the ebike plus me, as well as the amount of motor assistance for a given duration.

Switching out the tyres, tubes and front wheel would reduce the ebike weight by approx a modest 1-1.5Kg.
Even though this switch is more for lowered rolling resistance and some aero gains, which should use less motor battery to reach 15.5mph and give me a bit more speed for my effort above that speed... Maybe 1mph?

I'm very slowly trying to work on my weight, I'm on the verge of dropping under 93Kg for the first time in two years.
The inability to exercise like I could before long covid, combined with taking Mertazapine/Sertraline for just over two years didn't help me at all. Back in January I briefly hit 98Kg.
From summer '17 to September '22, I was typically 75-80Kg and 95% of my best 20mins power was approx 290-320W.

Like I wrote yesterday, 25mins of 250W assist uses ~40% of the 248Wh battery and on my recent first 50-miler ebike ride, I only engaged turbo when I was prepared to ride at or beyond threshold (mainly on 3.5 Strava cat4 hills 260-350 feet).
I could use less turbo assistance, which will dramatically increase the battery range/duration, but the big unknown is how long beyond the recent 50-miler's 3hrs10mins I can manage even with the huge help of an ebike.