7500s? In 2004? Throw those things in the trash where they belong. It's
always amazing to me how many people will cling to obsolete things for
years just because it is what they know.
Don't agree with this. For E1/T1 access these boxes are fine. Yes
they are long in the tooth but they are quite capable. I wouldn't spend
a huge amount of time or money trying to make them do anything else though.
Even a Juniper M5 will do 16 OC3's with line rate filtering and
forwarding. There are probably a dozen design considerations based on
requirements you haven't described, but if you're doing primarily sonet,
7600 isn't really the way to go.
Depends on what "primarily sonet" means.