I have those exact same specs...lol...we must be related somehow . I would lean towards the float tube if you plan on fishing mainly lakes and ponds...the inflatable kayak would be a good choice for mainly fishing streams and rivers. It can get awkward fishing out of a tube in a stream when you come across shallow water...plus you will have a hard time holding in a spot if there is any current with flippers. I would suggest looking into a pontoon boat. These are what we use out west when we fly fish for trout in rivers and lakes. They are really nice cause they sit you up out of the water, and you can use flippers, oars, or even a trolling motor. Here is an examply of what I'm talking about...
http://www.amazon.com/Creek-Company-.../dp/B0047E758K

Good luck!

-Rich