If you have a Intel CPU try to use his GPU as primary, so that will complete leave all memory on the cards. I hope that help you to make it run easier...
Its really matter which processor? I have AMD cpu on this mother board and don't have integrated videocard.
I mean it can be an AMD cpu with integrated video and INTEL cpu with integrated video.. what the difference ?
If you use the integrated GPU of the CPU you are leaving more free space in the 4Gb Card... all Megabyte is need to have the max value of the 4g-alloc-size. So if the primary is the integradeted GPU that leaves full space for the 4Gb... you still need the zombie mode but with more space in the memory of the 4Gb that will make more Mhs...