I believe in iOS8 (I haven't upgraded yet) that you can see exactly what resources are using how much of the battery. Shouldn't it tell you in there? Bluetooth would reduce battery life as it's very similar to wifi in the way it's always searching for a connection & sending/receiving data or packets.
Bluetooth virtually consumes nothing (we're talking in the microamps range) when not in a paired state, once you're paired the current increases to the milliamp range and then spikes during transmission.
I know this because I work on a product that includes bluetooth and I spent far too much time optimising power saving in both hardware and software to eek out every microamp.
Its also pointless from the point of view that other things on the phone (CPU/backlight) consume orders of magnitude more power than WiFi or Bluetooth, so you're basically kidding yourself if you think it makes any real word appreciable difference.
GPS is a a fucker though, our product has a GPS option and I have to send that into a deep sleep and operate it on a duty cycle because current consumption is high.
We also have a GPRS modem on board as well, and that has low power consumption when in idle (but on the network), nowhere near as low as bluetooth, but much lower than GPS.