I've written a few scripts - tempdb is obviously being hit quite heavily, with a massive IO spike across all 8 datafiles at that particular point. The top queries at that time - or rather before hand - are pretty small, and shouldn't really be causing an issue. Page life expectancy is still over an hour, CPU is only 27%, there are no blocks; the only red on my spotlight (vainly trusting technology!) is the I/O waits on tempdb.

As I say, there doesn't appear to be anything SQL wise hitting the system (there are surprisingly a few I/O waits for other DBs that nothing official is happening on).

Looking at the windows side of spotlight - again, nothing - solidly green throughout the period in question.

Hence my thought it may well be a SAN issue, rather than SQL.