...I placed a borrowed 8GB card in my S3 and it was recognized as 8GB. I didn't try to take any pictures with it though.
Your 8GB card was FAT32 ! (the thread was about the max. card size on the S2, S3 =! S2)
...It may be possible to exceed 4GB with FAT16 by hacking it to use a larger cluster size.
No, definitively not !
4GB with FAT16 uses already the max. possible cluster size of 64 KB !
The count of sectors per cluster is stored in a unsigned integer var, no bigger clusters are possible by the design of FAT16.