For an ecto who needs to gain mass fast, I would stick to 3x a week. You won't need as many calories to grow if you only do it 3x a week. Doing 5x a week makes it much harder to get enough food. If you want higher frequency than 3 times a week, you could just workout every other day, which would be about 4 times a week usually. You'll have to try it for yourself though.
I grew with both schemes, but my gains with 3x a week came a lot easier. However, I feel that the 5x a week scheme improved my strength faster.