I don't have an iPhone, I've not experienced BT drain; I've used my phone for 4-5 hours on BT headsets and maybe seen an extra 5% of battery go down, which is fine since I use less than a 50% charge per day.
The only time I've noticed BT drain was with Android phones. My Nexus 5 was horrible about random things spinning out of control and killing the phones battery. My current iPhone does not seem to have any of the same issues.
I have a Plantronics BackBeat Pro. Not the smallest headphones in the world (make me look like a Cyberman) but the battery lasts for 24h -- I've never had it run out on me. And the audio is great :).
