Hello. Since you are experienced with quadcopters, I would strongly suggest building a hobby grade quad. I personally have a 450 quad using a flamewheel clone frame. I get 20+ minutes with my 5200mah Multistar battery.
Here is a link to a 450 that is ready to fly ( provided you buy a battery for it ) but is also hobby grade where the replacement parts are easy to come by. I personally would want a better transmitter ( I use a Turnigy 9x ), but for about $200 you can get this baby flying.
Here is the type of battery that the product page suggests to buy. Of course with it only being 2200mah, the battery life is basically half of what I said above.
This is the battery I use on mine. Though be warned, I had to make frame modifications for it to fit nicely on my quad ( It's a lot bigger than it looks HUEHUEHUE sorry about that but it's true). It would definitely be a gamble to buy it and assume it will fit on the frame but on the plus side it would double your battery life.
It does not include FPV and any kit that includes everything you need is gonna be at least another $100.
This type of quad is what you are looking for, bigger, longer battery and can be upgraded to FPV.
*cough* 450 Flamewheel master race *cough*