[GrumpyDave]

FWIW, I was looking at the formatting-enabled version of the script last night. All of the time is spent in the single "duplicate characters..." statement so there's really not much to be done about tuning it. But I also have a warning for johnrover and anyone else following along...

It was taking 13 seconds to combine two small (5 line) emails with formatting. I decided to try combining some larger emails to see what would happen. The script ran for a minute or two and then the AppleScript timer timed out and left OmniFocus in a hung state that needed a force quit. After that I also had to cancel a sync that was hanging. No damage was done, but it's clear that using that particular script should be avoided. The plaintext version does work well though when unformatted text is acceptable.