It makes no difference. You have eight ports available on the RS2BL080. Four ports from each SFF-8087 connector. The expander backplanes each have two ports. Whether you connect each two expander ports to one SFF-8087 or two, you'll still be using four ports for both expander backplanes. One thing to consider, using a single cable would clean up the installation by not having four unused cables to contend with.