Default SD card format

Hey guys, if you guys realised that, the latest CWM allows us to format our internal and external SD cards into formats of our own desires like the ExFAT, ext2, ext3, ext4 and etc... But i would like to know anyone did it to format into your own preferences and how was the performance and so on. I personally tried ext4 on both my internal and external and i'm not sure whether it's slowing down my phone or what.
Happy to hear some responses from you guys as well