The Atlantis Surf-tamer 11/12wt loads with commercially available 11 and 12wt overhead lines, although some line brands run light or heavy. The new Atlantis All-around loads with commercially available 9 and 10wt lines (brands differ again, some 9wt lines have been light) but to get serious distances go with a 35 ft 10wt shooting head on the light action Atlantis with a slick shooter
The Loop 7116 sounds like a great weapon for the beach. The trick is to find out what grains per head length and taper the rod feels comfortable with for maximum casting distances and match the lines accordingly. Line ratings on spey rods are not very useful for overhead purposes as most of us have pretty much found out by now. I would contact LOOP and ask which lines they recommend for it, get the grains and head length of that line, and adjust for what you hope to use.
If they say it takes a line that is 450 grains over 50 feet, then it will probably only take about 400 over 35 ft. If you want to use a longer taper for overhead casting (sacrificing the short game) then maybe it will take 500 grains over 60 ft. Starting with a known sweet spot, go heavier for a longer head and lighter for a shorter head depending on what you plan to fish
Furthermore, floating / intermediate and fast sinking lines tend to vary as well.
IMHO this is because of factors like line diameter and density, air resistance and over "feel" of the line. A floating line of xgrains doesn't 'feel' the same as a hi-density line of exactly the same grains because of the way it cuts through the air.
Good luck with your quest. When you are ready to string up the "big gun" let me know how you plan to use it and I can steer you in the right line direction.