Much of this depends on your niche, how closely the products you promote with your niche and the responsiveness of your visitors are related.
Those affiliated companies that contact you should be able to provide you with the numbers you are looking for. You may want to take the numbers they give you with a grain of salt (so to speak). They may not be completely honest with you. But the numbers you request vary from one niche to another and between the types of products within a niche.
Are most of the page views recurrent visitors? If so, then you have an interested audience. That is gold if you market affiliate products that are related to the topic in which you are interested. Just do not overwhelm them with promotions or reject them. You want to spread the product links in that content with which you are already attracting them.
Check Google Adwords to see if the type of product you're seeing is selling. And to see how popular it is. If those statistics are low, there is not much benefit in that product. Enter the keywords for your product and also verify the additional keywords that Adwords suggests to find if your product is active or not.
You can get a lot of information from the Standard Data and Rate Service (SRDS). It is expensive to buy, but if you have access to a local library that has a copy, you can see it at no cost. However, not all branches of the library have a copy. For example, here in Indianapolis there is a copy for the whole city. That is in the main branch of the center.