Check with outfitters around the area for demo days where you will be able to test paddle a variety of boats. That is really the best way to get a feel for what they all do. You can certainly fish from longer boats. A good friend of mine in New England is a fishing guide who teaches people to spin cast from a standard cockpit sea kayak.
It might be too far distant for you (and maybe not soon enough if you are eager to upgrade for summer), but the Lake Arthur Regatta, just north of Pittsburgh and maybe half an hour from the Ohio border, is the weekend of August 3 and 4 and there are always outfitters with a range of boats you can try out on the lake (which is a great place to camp and kayak if you want to take a weekend trip up there sometime). I have to believe there are outfitters closer to your area that offer something like this as well.
I can tell you that I noticed a HUGE increase in my enjoyment of river kayaking when I went from my first kayak that was 14' long x 25" wide to one with a more vee shaped hull that was 15' (barely longer) but 21" wide. It seemed like half the effort for twice the speed. At first it had that "unstable" feeling that such hull differences create, but I soon learned that it was actually very stable even when leaned over. It got to the point where the older kayak seemed impossibly balky to me. But I kept it as a loaner, just as you are planning to do.
I have also found that people are usually pretty agreeable to letting you test their boats out if you meet them at put ins. And going on outings with a group (like the kayaking groups in most regions on Meetup.com) can get you meeting people with various models that they will usually let you try out.
4-place Boat Trailer
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