Just benchmarked website_agent as is on 3.5K events (which only got this far because I ran it for several days with the low uniquess look back of course - in 2 days time, it will have 70 events in it as the spurious ones expire)

Creation of the 3.5K active records: 0.4 seconds
Deduplication (involves a horrible double loop): 1.2 seconds
(I ran a few times, this was the longest)

So not pleasant but not a killer for an edge case until .

I got my github set up semi sensibly now (I actually do most of my development over on bitbucket), so I'll leave this PR as closed and launch another one from my dev branch.