I've been asked to look into the feasibility of using FileMaker to hold a
database of up to 5 million "assets", each with their own details (including
multi-record stuff like change history, etc.). I worry that FileMaker might
be unsuitable for this size of database? Does anyone have experience of
this?

Also, I should mention that there will be up to 200 users - is that
stretching things too far? Not all the users will be active at once -
although it's not inconceivable that they might all try to do something at
the start/end of the day.

What's the largest installation out there at the moment?