Mostly out of curiosity, have you not considered NetBlazers? (And if they
have been discarded, was it for technical or administrative/operational
reasons?) We're beginning to gain some experience with them, and I think
the folks at OARnet have been using them for a while. One of the most
significant factors in the differences we saw was whether or not you were
going to be routing to a remote LAN, or just providing SLIP/PPP for a
single node (Workstation/Mac/PC, etc). In the latter case, it used to be
that Xyplex was the most cost effective. This is what's in use at CMU for
SLIP service, and Tom Holodnik there has done a lot of work on distributed
configuration and authentication for them.
Gene