No ones answering you probably because this is a real easy question for you to answer on your own if you just search a little bit. But here I'll enable ya,,,,,,,,
Look
HERE.
6.1 is over rated you should just use the 3.16 and install codyppc threaded messages (Google Search) if thats all you want. From what I see thats Pretty much the only thing different between WM6 and WM 6.1 is threaded messages. Im sure there are other small differences..Most of the 6.1 roms are built from the leaked 3.16 rom.