What model of Memphis amp do you have? Do you plan on upgrading your car charging system (alt,battery,wiring,etc...)? Without knowing the specific model of amp and what upgrades you have made to the vehicle, I would recommend 4-ohm DVC or 4-ohm SVC. i recommend the 4-ohm because it can be wired to present either a 4-ohm load or 8-ohm(if dvc) load both which most mono block amplifiers can easily handle without huge power draws on charging systems.