A couple of weeks ago there was a thread on Meta on the topic (see Sort posts by merit spent).

One way to search for the most merited threads is to use the Merit Dashboard. If you go to a tab called “Rankings”, the right hand side block labelled “Top Merited Thread Ranking” sorts all merited threads (aggregate of posts within) by received sMerits and ranks them. You can filter by a specific section/subsection, and/or specify a date range using the filter at the top of the screen to, for example, see the most merited threads in the last month in the Bitcoin Discussion board.

Additionally, if you click on the thread name (page_title column), a popup appears allowing you follow a link that says “Go to a post with the thread” which does just that. It does not take you to the first OP within the thread, but that is easy to do by you once you are actually on the thread on Bitcointalk.It takes you to the OP within the thread.

It is true though, as said above, that threads swerve to and from in terms of content, so merited posts within the thread are often not precisely aligned completely with the thread’s OP.