Asterisk behind Cisco ASA 5505 with 50 phones?

Does anyone have call quality / performance experience for an Asterisk installation behind Cisco ASA 5505 with 50 phones?
I need to do such an installation but am uncertain if the firewall is going to cause problems on call quality due to adding latency to packets on its inspection cycles. I do not need or want to enable complex inspection algorithms or application-level inspections etc - the firewall is only there for basic network security.

50 users would require approx 5 / 5 MBit up/download on the internet line. The Cisco ASA 5505 official specs claim max. firewall throughput to be 150 Mbps “under ideal test conditions”. So should be very fine, but no idea how the ideal conditions compare to an Asterisk VOIP environment.
I do know that this device does cause a tiny bit of noticeable slowdown on internet browsing but have no experience what it will do on VOIP calls. The alternative would be a faster model, or is there any other handling?

Any experience appreciated.

The only time I’ve seen a firewall/NAT box really load down when it had Asterisk behind it is when Asterisk was generating a lot of dialer-type traffic, where the firewall had to set up and tear down a lot of NAT translations constantly. But the set up in that instance was a Cisco 2811 performing NAT functions for 3 separate Asterisk boxes and about 400 concurrent calls that had a lot of constant setup & tear down.

Having said that, the 5505 should have the horsepower to do it.