Richard, the first permalink in the example is a custom permalink - that's why it's "instead of". The second in the example is the default. The default achieves a higher Page Rank "out of the box" from what I've seen.
There are actually two separate issues at play here. One, which you asked about initially, is Page Rank. The second is search results. Page Rank is only one part of (Google) search results.
The search engine advantage to the first type of permalinks (which are not the default and are therefor "custom") is that if you are careful to use keywords (in the example, My Cheese Sandwich) in your post titles, you will end up with the keywords in the URL. This is supposed to improve search results by telling the search engines that your page is really really really about those keywords.
Page Rank, which is what you asked about, is a separate issue and from what I've seen the "?p=423" style standard permalinks perform better on Page Rank than the "05/23/my-cheese-sandwich" style. Where you will end up in actual search results (for Google) is a function of Page Rank and other variables, including whether you have keywords in the URL.
The only problem is that with Page Ranks of zero on your post pages compared to a Page Rank of 5 for your main page, Google would have to give a lot of extra weight to the keywords in the URL to make up for it. And as I wrote before, Page Rank isn't used by the other search engines but because what it measures is important to all search engines it's a good proxy for determining how other engines will view your page.