No experience with the deep six divers but we use the Dipsey Divers extensively on the Great Lakes for walleye and salmon. The size 1 dipsey is most popular and 60 - 70 foot depths are very realistic. They do have a newer MAGNUM size that I have not used but I'm sure 100 feet is realistic with that.
No idea how fast you fish for Tuna, but I'm guessing speed may be a problem for you. Great Lakes fishing with dipseys is done anywhere from 1.6 to a max of about 3.5 MPH. The faster you go the less depth it will achieve.
Get a copy of "Precision Trolling - Big Water Edition" by Mark Romanack. Mark and team have compiled extensive "Dive Curve" data for the most popular diving planars used in the Great Lakes. Data is included for mono / 30 pound Power Pro braid and 30 pound wire line.
www.precisionangling.com
I've caught Chinook King salmon up to 35 pounds on the dipseys but spend most of my time walleye fishing on Lake Erie. Dipseys are my "GO TO" summer presentation - often running 3 or 4 dipseys per side of the boat.
Another helpful resource might be the Great Lakes Angler Magazine website.
www.glangler.com
Steve