Enterprise Firewall for an ISP

Currently we are looking for Firewall
which can support satellite ISP
network. We are providing internet
service to multiple customers. Total
traffic is around 100 Mbps
(Uplink/Downlink. Total
sessions(TCP)around 30000 to 50000.
Current setup of Sonicwall 4060 with
HA hangs up intermittently eventhough
UTM options are disabled. Discussed
with various vendors resulted in more
confusion. Can anyone suggest any
enterprise firewall suitable for this
kind of application