The question you need to answer for yourself is:
How much gas do you need for your deco obligation?
Also... Don't make the dive without carrying enough gas for the dive. Relying on the boat as a gas location could be a error that could get you a chamber ride.
if you for some reason - you can't find the boat, and you've planned on using that 80% to complete your deco portion... would you have enough back gas to complete the deco if you didn't have that 80%?
Carry the gas you need to complete the dive. If that means slinging multiple stage bottles, then so be it.
Sometimes the best advice is the simplest advice...plan for the worst...hope for the best.
Thanks for the useful comments