When uploading large files to Orchard via http over ADSL, another setting that I needed to change was the connection timeout, which has a default of 120 seconds. This seems to override the settings discussed here and caused the connection to be reset. In IIS7 this is under the 'Limits...' section on the right hand side, for the specific site node, or 'set Web Site Defaults...' on the sites node.
The config section is:
<system.applicationHost>
<sites>
<siteDefaults>
<limits connectionTimeout="00:20:00" />
</siteDefaults>
</sites>
</system.applicationHost>
See also iis.net documentation