Good stuff guys, Once again, Thank you very much the guidance
After a more in depth search I found that Scientific Anglers also has a some interesting line that I missed in my initial search.
Bluewater Express in 500, 600 & 700 gn offerings. With the following line to Rod recommendations
Says here it is:
Formulated for better shooting
Stiff Tropi-core design minimizes Tangles
Extra strong core for Tuna & other big game fish.
Best thing since a pocket in a shirt...Buy some today & the fish will jump in the boat.....Yada yada yada
So it looks as if my initial guess of 600 grain might be OK after all. We shall see how it casts on this lance I have here. I also found a 500 grn Airflo Depth finder line in the pile of lines at the Fly shop. So I have that as a option too. I will test it out as well
Hopefully it will all come together by the end of the week. If my boat captain & the weather hold together I could be Tuna fishing Monday