Hi Walkin,
Memory foam and latex are completely different materials and are difficult to compare because they have different types of softness, there are many different types of 5 lb memory foam with different firmness levels, and the firmness/softness of memory foam can also change with temperature, humidity, and the length of time you sleep on it in the same position, but for most people and for most types of 5 lb memory foam, the memory foam would feel softer than firmer latex yes.
There is more about comparing memory foam to latex in post #2 here.
Phoenix