Our application runs in IE 10 mode, but a 3rd party server we access to display documents in an Iframe does not. We have found by using the Developer Tools that if we set the Browser Mode to IE 10 compat mode and Document Mode: IE9 that both our app and the 3rd Party is happy.
However, IE 10 seems entirely resistant to metatags in the web page:
<meta http-equiv="X-US-Compatible" content="IE9" />
or even registry changes:
iexplorer.exe = 9999 (decimal)
Running IE 10 on Win 7 or Win 2008 R2