Hi Bro
These Cisco ASA Firewalls (X Models) comes with built-in IPS. Hence, these equipment are built to provide low latency for applications, such as voice, video, and terminal services, because of its’ respective hardware throughput from 150 Mbps to 10 Gbps.
I do know that Cisco ASA 5580 series has a published spec of 30μs latency as a selling point for ultra low-latency environments. The entry-level ASA 5505 would not be close to that level. I'd assume that 50μs is out of reach for the 5505.
Perhaps, you could get more information here http://www.miercom.com/pdf/reports/20120514.pdf
Warm regards,
Ramraj Sivagnanam Sivajanam