My gut feeling is that Truss is being pushed by the ERG, so she has two years to not only embarrass us but do some damage.
Sunak seems to be the lesser of the two evils.
I am a great believer in never wasting a vote although spoiling it would send a message but would Tory HQ even care?
Abstaining/Spoiling might be seen as a 'vote' for Johnson. Even worse than Truss being PM will be Johnson walking around saying "Well the party loved me! They couldn't bring themselves to vote for anyone else!"