Internet Explorer extremly slow with html5

is there a solution for this?
if not, how can I work with html5="prefer" for all browsers but use flash with internet explorer?

Although it's not really a good solution I found a way to show flash in IE11 only:
html5:(navigator.userAgent.indexOf("rv:11.0") >= 0 ? "auto" : "prefer")

Anybody knows if there is a code to recognize all IE-versions at one time? I only use this because I have only IE11 installed, don't know if the bad performance also happens with other IE-Versions - although it would be strange if not...

ok, then I will test it on other systems. If it would be only an individual problem on my system I would not need to exclude html5 from IE11...or others