The big cache on the Q6 (8Mb) or the Q9 (12Mb) really helps them motor along under load.
The Q8's have bad FSB / Multi configurations for serious overclocking ... that would be an otherwise redeeming quality for cheap silicon.
If your going cheap and want to overclock get a full cache and a good multi / FSB configuration.
That's why the Q6600 was so good ...
If you dont want to overclock then just go to the cpu charts ... they are there for the n00bs who want to rationalise their purchase (reduce cognitive dissonance).
If you get a good aftermarket cooler and some sense you never have to spend more than $200 for a cpu that you can tweak and knock the latest top end cpu off the perch in terms of benchies ... and save $1000 (it's been a while since they were that much though ...).
I'm gonna get a Q9550 cos I can't find anywhere which sells a Q9450 and I'm put off by the 65nm architecture of the Q6600. Also I've seen that Q9550's overclock's are generally higher and I'll probably oc to 3.2 or so
According to Windows Vista and Windows 7 OS performance ratings, the Q8200 outperforms the Q9450. See this LINK.