well...I get the best ranks on my "tag"pages to be honest.
I think it also depends on how your slug is set up...the rule of thumb is that the words closer to the domain name, is considered more valuable...
for instance:
mysite.com/product/category
Is better than
mysite.com/category/product
when trying to rank for product...
depending on how your posts and pages are set, will play a role in how they rank.
however, google can pick up the differences between pages and posts on my autoblogs...
when I have too many posts schedule, google will show all my posts (12k+) as de-indexed in webmaster tools (just for a few hours)... (even though they are still indexed)
but there is always 23 urls that it never shows as "de-indexed" and those are my pages...
some of my posts are manually made just like a page would be made, but it still falls together with all the auto posts...
So there is obviously a difference in how they are viewed.
The strange thing is that my tags pages have very little if none seo if compared to pages and posts, yet they rank better. (maybe because it has a greater amount of relative posts on one page?)