450 items (users) are too much for an option list.
You should consider creating a browse page, with a seach function and not more than 50 users per page. After choosing the user(s) from there you return back to where you need it.
You could also write an template operator that fetches the user info directly from the database which will speed things up.
Hi,
do you mind sharing the operator?
I have 7000 users and about 5000 are in one group. Until now, i don't have to select users in a template dropdown, but it's just a matter of time.
BTW: Doesn't the workflow system (approval) use dropdown-list for users? Or does this use user groups?