There should not be any difference in performance between Ext2 and Ext3 formatted drives (there is a difference but it is in the security of the file structure and has nothing to do with how fast a file is read)
You say there is nothing changed on your network but since you are using wireless there could well be changes you are not aware of. Unlike a wired network where you are in total control a wireless network is very susceptible to outside influences - another wireless router or access point on the same channel as yours can, and will, cause interference which will cause packet loss requiring a resend and in many cases buffering.
We use WiFi Explorer from NutsaboutNets
http://www.NutsAboutNets.com on an Android tablet to check channel use and free channel availability at clients sites. This allows us to keep our clients on less congested channels. If you use that app or something similar at home you could well find the source of your problem (note I said 'could well', channel interference seems the most likely problem but it might not be).