I've asked a lot of questions leading up to this, so I wanted to share some of my progress.

The blue line represents the number of messages processed.  The background color represents the average response time.  You can see ticks for each hour (and bigger ticks for each day).   Hovering over any point in the graph will show you the numbers for that period in time.

This is super useful for "at a glance" performance monitoring as well as establishing patterns in our utilization.

Here is the query used:

SELECT
    mh.name                                  AS MessageType,
    COUNT(mh.name)                           AS MessageCount,
    CAST(AVG(ResponseTime) AS DECIMAL(5, 2)) AS AvgResponseTime
FROM
    (
     SELECT
            li.SessionId,
            li.Name,
            DATEDIFF(s, MIN(li.TimeCreated), MAX(lo.TimeCreated)) AS ResponseTime
       FROM
            (
             SELECT
                    SessionId,
                    name,
                    TimeCreated
               FROM
                    ens.messageheader h1,
                    HS_Message.XMLMessage m1
              WHERE
                    h1.MessageBodyId = m1.ID
                AND h1.TimeCreated > DATEADD(hh, -1, GETUTCDATE())) li
       JOIN
            (
             SELECT
                    SessionId,
                    TimeCreated
               FROM
                    ens.messageheader h2,
                    HS_Message.XMLMessage m2
              WHERE
                    h2.MessageBodyId = m2.ID
                AND h2.TimeCreated > DATEADD(hh, -1, GETUTCDATE())) lo
         ON
            li.SessionId = lo.SessionId
   GROUP BY
            li.SessionId) mh
WHERE
    mh.name LIKE '%REQUEST'
GROUP BY
    mh.name