I personally wouldn't use a 4/0 star drag reel for tuna.I'm not saying it can't be done but if I was going to go small I would look at a lever drag reel.Something that could take the heat of a nice tuna ripping line.Remember,its not a bass or bluefish.Tuna can make some pretty long runs and you wouldn't want your drag on a 4/0 to start burning up on you.If money is not an issue I would look into Shimano's TLD 25 or an Everol 12/20(size of a 3/0) 0r their 20/30's.(Size of a penn 30 inter.)I've owned them and found they are great little reels and full of cranking power and have smooth drags.My friend tricked out a Everol 12/20 to get 25 lbs of drag on it and the freespool spins forever.We've taken bluefin up to 94 lbs on the Everol 20/30 and handled them beautifully.My favorite are still the Shimanos,easy to service and their smooth drags can't be touched by anyone elses.Leave the 4/0's for bass and blues.
Last time I looked the Shimano TLD 25 WAS $199.00 and the Everol 12/20 was about the same.The 20/30 was a little more,I think 269.00 The super 12/20(thats all tricked out with bearing and solid frame) is around 300.00.
I too was able to get 17 lbs at full drag but rarely did I have to go past strike to take a fish.I'm talking inshore,not canyon.At strike you should have about 12 lbs. I always set them to fish alittle before strike,maybe 8-10 lbs.