I did this myself to get a v1 E61 upgraded to the latest v3. I used a Netherlands code to match my Australian E61.

I got it second hand from a mate. Unfortunately I didn't try the Bluetooth before I upgraded. It works really badly with my Supertooth 2:
http://www.blueant.com.au/supertooth2.htm

Volume goes in and out as the DSP tries to echo cancel I think.

The Supertooth worked perfectly with my old 6230 (which I lost). Blueant support were quite useless and tried to tell me the two different versions of Supertooth firmware were identical (so why have two different versions...). She also tried to tell me the Bluetooth audio can get out of sync and it's normal to have to reboot the phone regularly. Didn't have to with my 6230...

How's Bluetooth working for you sein?

Apart from that it's fairly good. Some stupidities with things like Mail for Exchange (and the commercial RoadSync)are annoying though. Bluetooth works fine for connecting to a PC. Occasionally I do need to turn Bluetooth off and on. In the quick playing I did with v1 when I got it, I didn't have any major issues though.