1. Length doesn't affect dampness. A board will get more or less damp with the tech used to build it. But yes, longer boards are usually more stable and have better edge hold because the effective edge is longer. Shorter boards turn and spin easier.
2. Both boards are far from being noodles. Both are very capable all-mountain directional twins. The Whatever is a bit softer and will do a bit better in the park, the Goliath will charge a bit better. But the differences aren't too huge, except for the WE having an extruded base and the Goliath having a sintered base.
Which ever you choose, I'd go with a 158 or 159.