As far as I am aware, LISTSERV(R) parms associated with your list's
definitions, has no knowledge per se of attachment sizes.  I believe it
treats it all as inline messages, for purposes of SIZELIM processing.

Of course system-wide (LISTSERV, SMTP client, SMTP server, and mailbox)
consideration could apply.  Download times are a function of the sum of
the various delays: queuing, raw data bandwidth, congestion retry, SMTP
design retry, server overload.

YMMV.

/Pete