We have GRF-400, [a 4 port version of the 1600] it initially worked
good. I like GateD and Ascend added some cool features. However we
had issues with scalibilty on the box. PPS performace isn't the
biggest issue you should be worried about. Management and support
is important. Managing the GRF isn't easy. Support from Ascend
wasn't all that hot either.
The ATM card on it has some real problems though. You can't add PVC's
reliably to it. We've heard that other IF cards have packet corruption
problems. Some updates [1.4.6] have broken just about every feature
in the box and we got to the stage that it wasn't good business
sense to continue to use the machine. Cisco and IOS have a lot of maturity
that Ascend, and I suspect people like Juniper, Torrent, NN, and Packet Engines
don't have. Meaning that one day it may work well but for the time
being its just to risky.