I just added a small http module to Rhino Commons. It is a very simple module that times how long it takes to process a page.
It only times the server-side processing, of course, but it is a great way to tell you where you need to pay attention.
It is using log4net to log the data, so you can redirect the output to a database, and from there, you can get all the data you want.

Configurating the module is very simple. Create the following table:

CREATE TABLE [dbo].[PagePerformance](
     [Id] [int] PRIMARY KEY IDENTITY(1,1) NOT NULL,
     [Date] [datetime] NOT NULL,
     [Message] [nvarchar](max) NOT NULL,
     [PageURL] [nvarchar](max) NOT NULL,
     [Duration] [nvarchar](50) NOT NULL,
     [StartRequest] [datetime] NOT NULL
)

Now, add the following to your <httpModules> tag in web.config:

<httpModules>
     <add name="PagePerformanceModule"
           type="Rhino.Commons.HttpModules.PagePerformanceModule"/>
</httpModules>

Finally, we define in log4net.config the appender configuration:

<appender name="PagePerfAppender"
             type="log4net.Appender.AdoNetAppender">
     <bufferSize value="10" />
     <connectionType value="System.Data.SqlClient.SqlConnection,
System.Data, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" />
     <connectionString value="Data Source=localhost;Initial
Catalog=Logs;User ID=logger;Password=logger;" />
     <commandText value="INSERT INTO dbo.PagePerformance
([Date],[Message],[PageUrl],[Duration],[StartRequest]) VALUES (@log_date, @message, @pageUrl, @duration, @startRequest)" />
     <parameter>
           <parameterName value="@log_date" />
           <dbType value="DateTime" />
           <layout type="log4net.Layout.RawTimeStampLayout" />
     </parameter>
     <parameter>
           <parameterName value="@message" />
           <dbType value="String" />
           <size value="4000" />
           <layout type="log4net.Layout.PatternLayout">
                <conversionPattern value="%message" />
           </layout>
     </parameter>
     <parameter>
           <parameterName value="@pageUrl" />
           <dbType value="String" />
           <size value="2000" />
           <layout type="log4net.Layout.PatternLayout">
                <conversionPattern value="%property{page_url}" />
           </layout>
     </parameter>
     <parameter>
           <parameterName value="@duration" />
           <dbType value="String" />
           <size value="50" />
           <layout type="log4net.Layout.PatternLayout">
                <conversionPattern value="%property{page_duration}" />
           </layout>
     </parameter>
     <parameter>
           <parameterName value="@StartRequest" />
           <dbType value="DateTime" />
            <layout type="log4net.Layout.PatternLayout">
                <conversionPattern value="%property{start_request}" />
           </layout>
     </parameter>
</appender>

The page_duration, start_request and page_url properties are added to log4net configuration by the http module.
Then, all that is left is defining the logger itself:

<logger name="Rhino.Commons.HttpModules.PagePerformanceModule">
     <level value="DEBUG" />
     <appender-ref ref="PagePerfAppender" />
</logger>

If everything went well, you have now got yourself a table in the DB that measures
how much it takes to serve each page.

Note: There is a small buffer (10 page requests) defined, to reduce the cost of the logging, so you would need to hit refresh a couple of time before you see the results in the table.