The big thing CM9 is missing that CM7 has is hardware acceleration. This means high end games don't work and videos like Netflix.
You can dual boot as well, with CM9 on the internal and CM7 on an sdcard.
As for bluetooth, neither version has this working.
Device: Samsung Galaxy Nexus
Android Version: 4.1.2; AOKP Build 5
Device: Motorola Xoom WiFi
Android Version: 4.1.2; Eos Nightlies
Device: Samsung Moment
Android Version: 2.2.2; UberMoment 1.3.4
Other devices I am familiar with:
HP Touchpad | HTC Droid Incredible | Motorola Droid X | Motorola Photon | Nook Color | Nook Tablet