bcrypt at 10ms only being 300 times slower would indicate you can only try 30,000 MD5 hashes per second -- which is incorrect. Using a GPU based cracker on a current generation top-end video card you can calculate over 300 million per second.
Bcrypt at 10ms is 3 million times slower, not 300 times.
There is no such thing as a GPU based bcrypt hasher because it woudln't be - from my understanding - any faster then a CPU based one. Not all calculations are able to be sped up through the use of a GPU.
So I'm comparing the fastest you can do bcrypt hashes (100 a sec at that work factor) vs the fastest you can do MD5 hashes (250 million per second)
Bcrypt at 10ms is 3 million times slower, not 300 times.