Knock at hot startup

My 3sGTE, though now due for it next 3k oil change I admit, knocks like
its mains are shot but only on hot startup - i.e. after a motorway run,
or when shes been up to temp for 30mins plus. She naturally runs very
hot with the turbo, so im guessing is hard on the oil (hence i use
10-40 fully synth).

When left for days on end, weeks even, a cold startup will be more or
less silent, after a couple of minutes as the idling starts to settle
nearer 800 she gets a slight load independant knock but only as much as
you'd expect after 100K miles, and that soon goes when she warms a
little. But the hot one is a proper clackety knock. I always make sure
to leave the car 20 secs before driving away, to limit any damage.
I'm gonna fit a pressure gauge but the oil pressure light never fails
to go out right away.

So im thinking through the likely causes and all i can see is that the
oil is getting too thin when it gets hot. If I use it to the point
where it would knock if restarted hot, but leave it to go cold before
restarting its fine again.

Who agrees? Engine is coming out later this month for a clutch change,
i think I'll check other things out - bearing condition etc.

J