again, like i said in my how-to, the 5mm will require shaving the housing to accomodate the larger leds. i will not tell you how to do this only to save my own arse.
you shouldnt get a fast blinker syndrome as long as you have one large bulb on the front working. you need to have the 1156 bulb as your turn signal. make sure your tails arent out as well.