Using Page cache is normaly helpful for providing better performances on server. And serving cached pages from database helps the

servers to work faster.

in drupal When caching is turned on the HTML output of a page is stored in the cache_page table, so one query is enough to retrieve the HTML output for display instead of hundreds of queries on pages with many blocks, links, etc.

PageRank is a link analysis algorithm used by the Google Internet search engine that assigns a numerical weighting to each element of a hyperlinked set of documents, such as the World Wide Web, with the purpose of "measuring" its relative importance within the set. The algorithm may be applied to any collection of entities with reciprocal quotations and references. The numerical weight that it assigns to any given element E is also called the PageRank of E and denoted by PR(E).

To check your Page Rank just provide your In below textfield and hit submit button.