Hi,
My question is my topic and also another one:
does NAT reduce speed?
Theoretically, 65536 hosts could be NATd through one IP, realistically, around 4000. This is of course assuming your firewall specifications have enough ram/CPU to manage the connection tracking database as well as Internet throughput to handle the sum of all traffic.
Above response also applies to your second question; speed has many variables. The number of simultaneous connections that must be tracked will have some impact on the CPU and thus, the maximum aggregate throughput through the firewall. How powerful a CPU or how much RAM will determine if that impact is noticeable or of any concern. Note that firewall routers do not need to be supercomputers (or even desktop PCs by today’s standards) for modest sized networks. As usual, YMMV.