You would be surprised how much can be "parallelized" -- most software is designed for serial processing because that is how most programmers have been trained to think. But the number of tasks that an ordinary computer does that are ESSENTIALLY serial is small.
I agree with you though, that cooking up a benchmark that maximizes the performance improvement can be very misleading.
Cool screen name. It's been 15 years since I read those books, I'll bet a bunch more have come out since then.
IMO, the later ones were weak re-hashes of the characters. If you've read the first half, the second half can be given a pass.
Unfortunately, no. Keith Laumer, the author of the Retief series died in 1993. There have been a few posthumous releases though. Hopefully, there will be more unpublished works released.