base2 

I see nothing wrong with those numbers.
It's good to have the data from an actual measuring device. I suspected that the e-assist of the cargo bike was influencing Stravas estimates.

How far those watts carry you is a function of weight. So the real question is how long can the effort be sustained? If the curve gets substantially flatter you may have a reasonable shot at making your goal in the allotted time.

There are online calculators for this sort of thing, but there is nothing quite like raw grit & determination come event time.

Have you tried doing recon yet? Google Earth, Google Maps, could help you familiarize the twists, turns, way points, land marks, etc...in your head before the big day. I'm sure there is a write up or 2 on crazyguyonabike, or elsewhere.

I find that breaking a climb (or any challenge) down to bite sized chunks keeps the task managable.

Inside my head you would hear things like:
"Get to this turn."
"Get to that switchback."
"Get to that overlook."

I also find that constantly asking myself what I need:
"Am I thirsty?"
"Am I hungry?"
"How's my heart rate? Stable at 180bpm?"
"How's my pedal stroke? Round? Square? Like pistons?"
"What is my RPM?"
"Is this the right RPM?"
"How is my position?"
"Is holding this position accomplishing what I want?"
"Am I breathing?"
"Can I be breathing better?"
"Can I exhale deeper?"
All of these questions and many more help to keep my mind both occupied on the task at hand but also how to make the right decisions & stay in control of the situation & myself.

Climbing is a mental game, not a physical one.

Sometimes things don't always go as planned. But if you don't go, you don't make an attempt, then in the process of avoiding failure, you've lost the opportunity to succeed & all the effort? It's all been for nothing.

I've aborted climbs &/or stopped/paused rides for heatstress before it turned to heatstroke many times when the answers to the above questions all start coming back wrong. That yielded new questions: "Am I dizzy?" "Why am I dizzy?" "Am I sweating?" "Why am I 'not sure'?"

During the 2018 Seattle to Portland double century in 90 degree heat, I stopped the ride for an hour just to sit in the shade, 30 miles from the finish then spent another 45 minutes drinking water at a nearby gas station until I started sweating again. Once satisfied I could regulate my body temperature again, I continued on. Similarly, the summer before, I took a nap under a tree for an hour along Highway 97 before climbing Blewett Pass for the second time that day. A similar situation occured 15 miles into my attempt at Hart's Pass & I was not satisfied I could regulate my temperature, so I made the decision to turn back. There is no shame in either outcome & I am proud to have made the right call by keeping mental focus & constant re-evaluation.

My suggestion is the power numbers are a tool. Nothing more. A metric to gauge your current performance against what you know is sustainable. When you make your climb attempt, have power, heart rate, & rpm data on a screen & be constantly asking yourself if what is displayed is sustainable & what is the right decision to keep it so. Keep your mind focused on the questions above & before you know it you will have either made a tremendous accomplishment or a valiant effort you can be proud of.

You still have won either way & no matter what happens you still have sharpened the tools in your mental toolbox strengthend yourself in some manner & added value to your life story in the process.

No one can knock you for that.