List three factors need to consider when upgrading processor?

Clock speed, MIPS (if such information is provided), how many cores, and socket.

But all depends on what you really want to use it for. You won't need more than dual-core or a quad-core if you're just gaming (most programs and games don't use more than one).

However if you're into the content-creation industry (video editing/producing, YouTube or other video sites) or if you run a business that requires business-grade servers, then more cores will definitely help with rendering times and load balancing.