I need some advice on RAM configuration for a Mac Pro 3,1. Does anyone knows if there is any disadvantage in mixing 8GB (4GBx2) of memory with 4GB (1GBx4) for a total of 12GB? The 4GB sticks would be placed on different risers and the remaining 1GB sticks two on each, giving 6GB per riser. Is that advisable? Thanks in advance.