I have owned mulitiple Parkers with several different tank configurations.
A split tank is ok if you primarly fish squid. You are limited on fin bait capacity with a split tank. You get a much larger swimming area in a single tank. Fin bait needs as large of a swimming area as possible for capacity and life. Its deffinately a trade off. A large enough single tank (65gal or more) will carry both baits, just not as well as a split. The squid will hunker in the middle and the swim bait will swim to the outside. Whatever you decide make sure you get a oval tank. The bait uses more of the tank with an oval compared to a square or retangular design.
I have a 2520 with a single 90gal tank. I had a split 85gal and the single 90 carries 3x as much fin bait due to the large swimming area. Its hard to fill the single 90 with bait. As they say the one with the most bait wins.
Randy Wood in the original owner of offshore tanks. He is back in the business of making tanks again and has new desgins and capacity. It would be worth your time to give him a call!
Randy Wood 714-476-3827
Good Luck!