QUESTION: Is there an ideal physical size for using dual SSD configuration?

For example, do two 7mm drives, such as the Samsung 840 Pro, fit better or worse than two 9mm drives, such as the OCZ Vertex 4?

I'm concerned that in a space so small using two 9mm drives may not fit. Or, likewise, using two 7mm drives may leave too much room and potential for vibration noise.

Anyone have experience in this matter?