I use ISO 400 at EI 250, so even in bright sun, I shoot 1/300 f/16 (my top shutter speed).

Even at rated speed you should have 1/400 f/16.

Double-check your metering technique if you are getting 1/2000 f/8.

Indoors, I don't know. Maybe someone will strike a match. I've been known to use other people's flash (use B and synchronise your shot with somebody else taking a flash picture)