Memory accounts for a considerable portion of the total power budget and area of digital systems. Furthermore, it is typically the performance bottleneck of the processing units. Therefore, it is critical to optimize the memory with respect to the product of power, area, and delay (PAD). We propose a hybrid cell assignment method based on multi-sized and dual-Vth SRAM cells which improves the PAD cost function by 34% compared to the conventional cell assignment. We also utilize the sizing of SRAM cells for minimizing the Data Retention Voltage (DRV), and voltages for the read and write operations in the SRAM array. Experimental results in a 32nm technology show that combining the proposed hybrid cell assignment and the cell sizing methods can lower PAD by up to 41% when compared to the conventional cell design and assignment.