Where do I catch and handle maxAllowedContentLength exceeded in IIS7?

I have an aspx page where I’m allowing a user to upload a file and I want to cap the max file upload size to be 10MB. IIS7, .NET 3.5. I have the following configured in my web.config file:

<location path="foo.aspx">
    <system.web>
        <!-- maxRequestLength: kbytes, executionTimeout:seconds -->
        <httpRuntime maxRequestLength="10240" executionTimeout="120" />
        <authorization>
            <allow roles="customRole"/>
            <!-- Deny everyone else -->
            <deny users="*"/>
        </authorization>
    </system.web>
    <system.webServer>
        <security>
            <requestFiltering>
                <!-- maxAllowedContentLength: bytes -->
                <requestLimits maxAllowedContentLength="10240000"/>
            </requestFiltering>
        </security>
        <handlers accessPolicy="Read, Script">
            <add name="foo" path="foo.aspx" verb="POST"
               type="System.Web.UI.PageHandlerFactory"
               preCondition="integratedMode" />
        </handlers>       
    </system.webServer>
</location>

I have a custom error handling module that implements IHttpModule. I’ve found that when maxRequestLength is exceeded, HttpApplication.Error does indeed get raised. However when I play with maxAllowedContentLength, the HttpApplication.Error event isn’t being raised and the user gets redirected to a 404.13 page. I've attached with Visual Studio with first chance exceptions turned on nothing is being thrown.

My first thought is to check the header content length in an earlier event – are there recommendations/best practices of where I do this? PostLogRequest? EndRequest?