Well, the Tuniq hasn't had a lot of reports of extremely uneven bases, like the Thermalright Ultra 120 Extreme has. Still, if you've got nothing better to do, lapping the base will provide better contact to the cpu regardless (as long as you do it properly).
Check to see if you need to lap by:
1) Razor blade / flashlight trick: Set your heatsink down so the base is pointing towards the ceiling. Aim a flashlight across the base so the light shines at you. Place a NEW razor blade across the base and see if you notice any light passing between the base and razor blade edge. If you do, you might want to consider lapping. Check horizontally, vertically, and diagonally to be sure.
2) Water droplet / glass test: Same orientation of the heatsink as before, and place one or two drops in the center of the heatsink. Take a flat piece of glass and lay it over the top. If it doesn't spread evenly, there's a concavity/convexity of the base, and lapping should be done.
Edit: Tiramisu, you might want to update your specs now that you've got that beauty of a quad