Hi,
Each version of IE can have many different useragents associated: (http://www.useragentstring.com/pages/useragentstring.php?name=Internet+Explorer).
If you want to only allow IE version 8 and above, maybe you could look that the user agent contains "MSIE 8.0" (for IE 8), "MSIE 9.0" (for IE 9), "MSIE 10.0" (for IE 10), "MSIE 10.6" (for IE 10.6) and "rv:11.0" (for IE 11). These should only exist in the relevant versions.
To use them, try:
expr { [mcget {session.user.agent}] contains "MSIE 8.0" || [mcget {session.user.agent}] contains "MSIE 9.0" || [mcget {session.user.agent}] contains "MSIE 10.0" } || [mcget {session.user.agent}] contains "MSIE 10.6" } || [mcget {session.user.agent}] contains "rv:11.0" }
May require a bit of trial and error!