Up to how many nodes Drupal can handle without affecting performance?
It very much depends on your hosting and server configuration. 

For example one of the projects I worked on handled without performance issues about 10 millions of nodes. But it lived on a cluster of 4 dual-core servers with lots of memory on each, and the cluster was behind load balancer and reverse proxy caching (Varnish). 

On another project I had performance issues after something like 1000 of nodes, that was a shared hosting.