Keef,
Not sure I would take your approach to using Spamcop, i.e. as a pre-filter.
I use Spamcop to report spam after it has been received, and in that function, I've seen no change in recent weeks, it still works just as well.
For spam filtering, you really should just seek out an ISP (or webmail service) with good spam filtering.... then the one or two that make it through after that you should report via Spamcop.