We examine the effects of modifying the Co hard layer thickness of Co/Cu/Co spin valve submicron pillars with current flowing perpendicular to the plane. The magnetoresistance(MR) ratios and switching currents show complementary behaviors. As the Co hard layer thickness is increased, the MR ratio shows an initial increase with a peak around 21 nm. The critical switching current shows a dip around the same thickness, which is close to the spin diffusion length. The product of the MR ratio and critical current density is about a constant independent of the Co hard layer thickness. Thus, we provide an approach to achieving maximum efficiency (MR ratio) and minimum consumption (critical current) for a practical device.