Thanks for the feedback everyone.
I took the list as it is in the OP in the end; I just couldn't find a way to bump a unit up I was happy with. It ended up costing me the first game as I wiped out my opponent but the scenario rules meant that only the secret missions and scenario conditions counted. My opponent had killed the Flamers, so we drew.
As it happens I ended up in 3rd place overall with the same TPs as 1st and 2nd, behind 2nd by about 1000VPs. It's pointless speculating about what would have happened if I'd changed the list to protect against the mission that cost me the first game, as my opponents would all have been different from there out.
I've posted a short report
on TWF.