I started fishing out of an Ultimate 14.5 solo last spring. It's a great boat - very stable and more like a canoe than a kayak. Easy to transport and paddle, tons of storage room and an extremely comforable seat.
I am not comforable standing up in it because it has very little freeboard. When I have tried to stand I felt like i was going to flip very easily. I am 6'5 and have a high center of gravity which certainly doesn't help.
I have not practiced standing in a 'safe' environment such as a pond without waders on. That might help.
The only other downside of the boat is it will take on water from chop and wakes due to the low freeboard/open design. Good to have the bilge pump ready at all times.
I am toying with the idea of aftermarket pontoons this spring. Like you, I really want to be able to stand and sight fish from it. There are plenty of places where the kayak would be perfect for that.
The wavewalker looks very stable but seems like it could be cumbersome to paddle and car-top. The seating looks uncomfortable as well.
The freedom hawk might be the ticket. I would love to hear some first hand reviews about it.
Google slo-mo boats as well. In hindsight I probably woudl have gone for one of those had I known about them.
Overall I am really glad I bought the kayak. It's a lot of fun and has opened up a bunch of places I could not fish effectively on foot.
Hopefully some other yakkers will provide some feedback as well.