Robert_Charlton - 7:42 am on Jun 23, 2013 (gmt 0)
...does the on-page SEO benefit of site A get transferred in a 301 redirect or does only the link juice get transferred?
No, the on-page content of a page on site A effectively ceases to exist when you 301. Only the link juice gets transferred (and it's been guestimated that roughly 15% of the link juice is lost).
Note also that when you 301 a page, the links that were on that page cease to exist, so the outbound link juice from links that were on the page disappears as well.