During the forum maintenance, I managed to reproduce the issue with 400 battle size, so that's not a safeguard. What I saw in thread dumps was 20% of CPU time alloted to
CampaignState.advance and 15%
Econ.advance (sp?) over about an hour after first experiencing the slowdown. Turning off campaign map "speed-up" smoothed my FPS experience, but still ran noticeably slower than before that "big battle" event. This time, with Vayra's off, it wasn't an HVB, and it wasn't an IBB - just a regular "Personal Bounty" and a Vengeance Fleet.
Trying to bore down onto the higher rated
advance elements did not yield anything I could understand or associate with anything in particular.
Edit: Here's the saved
snapshot.
Edit²: After 3h, 30 battles, and a excruciatingly slow campaign map traverse with slow menus...
... I now have 3 hours of CPU sampling, and these are my "hotspots":