You might want to add a low-weight electric assist. My favorite is an Austrian one, the Add-E. This uses a battery pack that looks like a water bottle, the motor simply rubs the rear wheel and creates no drag when it's not working, and can be easily removed from the bike. The best part is that only weighs 2,4 kg.

One of the funniest features is that it can provide 250W or 600W. The 600W version can thrust your ride up to 45km/h, making your ascent stage real quick.

Since you might have to deal with headwinds while riding a loaded bike, the assistance might be a good idea.

And the best part of the Add-E is that since it can be removed easily, you can use your bike without the added weight anytime!

Yes, I'm a fan of the little thing.
add-e ? The retrofit kit for your bike ? Technical information