I actually tried to at that time, but failed to generate the upgrade plan, and failed to go return to Upgrade Advisor afterwards.
The whole My AutoSupport website feels pretty awkward to me actually.
Risks and warnings keep poping up, disapearing and coming back.
I can't view half of my systems, even though I tried to re-register them correctly with support multiples times.
And it's outrageously slow connecting from France.
Anyway, I went for a new upgrade yesterday (8.1.2P4, for all the SMB2 fixes), and managed to get the upgrade plan out.
There were some useful directions in there indeed, so thanks for heading me back to it.