I am not familiar with the CPU that is in the CRS125 but noticed that it’s only 600 MHz. My internet connection is a FIOS 50/15; might a couple videos streaming in HD and some downloads. Not much routing required with the exception of NAT traffic and some lite VLAN use.
What can I expect from the CRS as far as performance on a small network with typically 5 active users?
So far I’ve had it setup as a switch, no time to play with getting it setup as a gateway. 
I’m curious what the upper limit is myself… I currently have 15/1 and at full speed only hit like 5 to 10% CPU. Looking at upgrading my line to 100/20
That’s actually the same reason I’m probing for some information. My area was just upgraded to support 100/20 and with the current CPU I wasn’t sure of it’s capabilities. 
Where are you located?..
The rb2011 wich has the same cpu and memory can do a throughput of ± 270/250Mbit with firewall, not to many rules and NAT. This is not based on the official test so it might differ a bit this is from somebody with a 500/500 connection I know. Mikrotik used to have the throughput numbers on there product pages but I cant find them.
I know a lot of people who are using rb2011 on a 100/100 line without any problems so I think your good on your crs125.
On rb2011 I have 6 subnets, with simple queues to 10/10 mbps and rules to drop any traffic between local networks.
CPU stays less the 50% so far… CPU goes up only when queues are working hard in “red” to keep the limit