There is no such thing as a hardware firewall and don’t ever let anyone tell you anything different. Hardware cannot function without software running on it, whether or not it’s firmware/embedded or saved on some type of media. Now, with that said, some systems have been optimized for throughput for routing/switching packets quickly on their interfaces so that access speeds are faster (ASICS and hardware accellerators). That’s nothing more than hardware thats been specifically designed to perform a function more efficiently.
That being said, I don’t have experience with the Netscreens, but you will want to compare their throughput speeds vs. how secure they are to determine if that’s what you want to use. Don’t sacrifice security for speed. What good is a firewall that runs at OC-148 speeds but only correctly evaluates 1 out of every 6 packets? Look for comparison studies from someone like Network Magazine or an independant lab to get numbers. Sorry, I don’t have the time to search on it right now.
Hope this helps,,