A 4 or 8mp camera has the pickup to support but may have poor lens, chipset etc. You mention your 5k screen I'm assuming this has a price point etc. Buying cctv on frontend pixel count is like buying a car based on bhp alone,meaningless. A decent 2mp camera will give a better image than a cheap 8mp etc etc. Many people compare phone pickups to what good dslr can do. Just bear in mind it's never about pure specs