Possible GPU upgrade for Precision M4600

Hi,

I'd like to get feedbacks from users that have successfully upgraded the GPU on their Dell Precision M4600 beyond the manufacturer available cards. Could you please let me know what card you used, if they are branded (HP, Dell, or others), what kind of BIOS you are running and if you ran into any issues! I am trying to find out definite answers about what can be done on this computer.

Thanks!!!