Thanks for your response. Sorry i should've mentioned that we are deploying to an XP environment, hence why we're not considering IE9.
Without knowing what your timetable is for deployment have The Powers That Be considered support for XP ends in April, 2014? You are 19 months away from MS pulling the plug and offering no further support, and depending on your sector, you are in for a compliance nightmare. It doesn't really make sense to develop a solution and pursue a plan that you will be FORCED to abandon and redevelop almost the day you deploy it.
I know you're probably not the person who actually makes the decisions and are probably just the poor sap left to clean up the mess, and all these arguments have already been made and rejected.