Firewall Rules & Performance

I see that most of the routers have a listing of their speed performance with 25 “simple” firewall rules. What is considered a “simple” rule, and would 40 rules cut the performance dramatically?

Beside firewall rules, what else can slow the performance of the router?

I have around 40 lines of rules, and I am wondering if this is hurting my performance in any way.

Thanks.