> Whilst testing some queries is there a way to clear the DB (and
> perhaps OS) cache *completely*.
>
> I've tried disconnecting from the database

This will clear DB cache, but not an OS cache

> and restarting the service,

This is not necessary

> but the first 'cold' run of certain queries still run quick - unless
> I completely reboot the machine.

This is because of OS cache

> Also, is there a way of seeing the plan to be used *without* actually
> going onto to run the query against a large table?

Just prepare it and request a plan

Regards,
Vlad