Bottlenecks must have a context to help find out what is causing the problem. In other words, tell us the flow so we can find where its slow.
These days, traditional hard drives seem to be getting a lot of fingers pointed at them. Think about an SSD to speed the old laggard up. That will solve a bottle neck with your favorite game booting, but it won't help with faster frame rates. For that you need a better video card, or in some cases, a faster CPU.
So, the bottom line is, no general guide to bottlenecks (maybe some of my more knowledgeable brethren can lend assistance).
If you want to find the relative of any given component, or to see if your configuration is operating at peak performance, here is a link to Passmark Performance Test
, which will give you relative metrics for thousands of components.