What handset has the longest battery life with constant bluetooth drain (IE listening to music)

I've got some bluetooth headphones on order, should be arriving soon, but while I'm waiting I'm starting to think my R6 will choke at the thought of something actually using the battery. Esp. since I got one of those micro dongles for the PC and was having a play around, R6 was (according to the icon anyway) fully charged, but sending a file actually killed it O_o.