[exim] How well does lsearch scale on high volume servers?

For example say my /etc/userdomains file has 10,000 lines(domains) in
it. Or say my /etc/aliases has 100,000 lines(aliases) in it. How well
is exim going to be able to perform with these files being this large
when it needs to search? Are there better options to use?

~ShaunR