My personal view !!!
If you have a good source - a high quality intercom - and not least
good quality speakers - nothing can compare to that.
But playing mp3 etc - is from the start - crippled.
mp3 is already compressed digitally, and feeding it into a Bluetooth system - will again try to compress it - and also need to decompress and do a dig2Analog conversion.
The mp3 is not feed directly as binary data to the bluetooth - it will be dig2ana converted - then ana2dig - finally dig2ana again.
All this manipulating of the data - will cripple it - more or less.
But - riding the bike will give you quite a bit of wind noise - and then you will probably not hear any difference.
I have now tested 3 different bluetooth systems, but I'm now on wired system om my GTL
Don't ask me to range the different ones, as they all are different in all aspects. Not only in sound quality.
It's all about what quality you want or need when riding ?!?
And - using HIGH quality speakers and correct mounted in the helmet is probably more important.
Personally - I feel that it's a bit premature to go into full bluetooth now.
It will upgrade and new protocols will be made - to make it "the" perfect system for the bike.
I think it will take another year or two.
Then I will probably switch to bluetooth, but not now !
I'm using bluetooth from the GPS and cellphone - and for that it's good enough, but not for music - at least not for me