If the chart size isn't changing, wouldn't it be faster to see if the chart has already been rendered and simply call setXMLData on the original chart?
This is normally what we do - we have pages with 35 charts on them - I wouldn't want to take the time to dispose them all.
So:
if ( mychart) {
myChart.setXMLData(responseText);
}
else{
myChart = window.myChart = new FusionCharts("../FusionChartsBroad/AngularGauge.swf", "myChartId", "350", "200");
myChart.setXMLData(responseText);
myChart.render("chartdiv");
}