[exim] exim capabilities fo 10-30 K email accounts

Hello group,

I was wondering about deploying exim on a server that would handle 10-30
thousand ISP customer's accounts.

I realize exim can likley handle this, but I was wondering what kind of
server you'd all recommend (1,2 or 4 processor? ram? HD space?)

Is it realistic to assume this level of functionality on an exim server
that may also be hosting maybe a couple hundred small sites (IE the ISP
customer type sites)

Formerly I've used qmail to do this but I'd much rather do Exim if possible.

TIA for any insight :)

Lee.M