Have you moved any of the problem apps to the SD card? It is a slower storage method than internal storage. If it is a low class (2 or 4) SD card, the transfer rate is very slow and could affect performance.
As to the web crashing, I have no idea or explanation for that. That should have absolutely nothing to do with the card.
The Commandments of Android
1) Open RAM is wasted RAM - Don't use Task Killers
2) Cheap devices are cheap for a reason. Don't expect high end performance.
3) Boot Loop = Wipe.
4) There are no viruses for android.