I don't think the CPU detection has really changed since the beta, though I'm not positive on that. It sounds like the beta also didn't detect your cores properly, which is why you had the override on. This may be due to XP x64, as I'm fairly sure Core 2 Duo's are generally detected properly in other cases.
With 2 cores you should only be rendering with 2 threads, definitely not 7 or 9, so I'm confused about those numbers. I would use the override, set min threads to 2 and max threads to 2 and re-test. Improvements in detection of the number of cores may come in the future, but we've found it a pretty hit-or-miss thing, especially between OS's. It's also a challenge because some CPUs like Core i7's actually have non-physical cores that can still be treated as legitimate threads.
- Oshyan