using the suggestion of manually adding "mb" behind the memory size in your configuration file (as suggested in this thread: Android: failed to allocate memory ) (located at: %USERPROFILE%/.android/avd/name-of-your-avd/config.ini) has solved the 768mb problem here!
example that now works on my win7 x64 ultimate os -with- dedicated gpu;
avd.ini.encoding=ISO-8859-1
hw.sdCard=no
hw.device.manufacturer=Google
hw.mainKeys=no
hw.lcd.density=320
hw.accelerometer=yes
hw.dPad=no
hw.cpu.arch=x86
skin.name=720x1280
abi.type=x86
hw.device.hash=1197498893
hw.trackBall=no
hw.device.name=Galaxy Nexus
hw.camera.back=none
hw.sensors.proximity=yes
hw.battery=yes
disk.dataPartition.size=512M
hw.gpu.enabled=yes
image.sysdir.1=system-images\android-18\x86\
hw.audioInput=yes
hw.sensors.orientation=yes
hw.camera.front=none
hw.gps=yes
skin.dynamic=yes
skin.path=720x1280
hw.keyboard=yes
vm.heapSize=128
hw.ramSize=2048mb
I have tested this on two machines, my desktop and laptop both running Windows 7 X64 Ultimate
The Laptop has an Intel I7-4702MQ with 12GB ram and GeForce GTX765M
The Desktop has an Intel I7-3820 with 32GB ram and has Ati 6950 in Crossfire and an Nvidia GTX560Ti (normally for physx).
The desktop only has issues in reliably starting the gpu acceleration while using crossfire, other then that i've had no issues with the emulator at all and even managed to assign 4096mb RAM with a 256VM Heap (however increasing the VM-heap above 128 seems to slowdown emulator initiation tremendously here)
On the desktop i also tested the 4096MB setup while even using a RAMDISK but this didn't increase performance too much.
Best settings overall (in my experience) in startup and responsiveness after just a few tests;
2048 with 128mb VM Heap size, gpu acceleration enabled.
Hope this helps out others!