Hi Krishna,
When you are using GNS, actually what is happening is that your PC CPU is acting as router's CPU. So as you keep on adding router and keep on configuring routing processes, your PC CPU will be going higher and higher.
Yes, EIGRP should be also affected, but it depends which resource is getting the available CPU cycles and which are left out.
Let do one more experiment. Try running OSPF in your topology too along with EIGRP and BGP and see what happens with the OSPF neighborship. At that time we can also try/check how much EIGRP neighborship remains stable.
Also, you can do one more experiment. Just run 2 routers and check the your CPU utilization. Configure your BGP scenario along with EIGRP.
Another experiment can be pinging end to end when CPU utilzation is less ( If you haven't found idlepc value so far, then in just try it with 2 router scenario) and try pinging when CPU utilization is high ( say scenario where you have 7-8 routers with some routing protocol).
Regards,
Smitesh
