RE: 30 minutes flight time from my Super Sportster EP!
I suspect that what you left out is that with the change in prop there was a change in throttle management. Also, you never stated what the capacity of the battery was that you were running down in 6 minutes. It's the little things....
I bought the T-600 setup from Tower originally. It came with a Master Airscrew 10x8 E-prop. That setup wouldn't pull a sick cat out of the sandbox. I bought the S-600 motoer separately, later. It flew the model pretty well on 8 cells but the flight times were short. If you were watching the $$ you could have bought the S-600 pieces separately and saved, plus spec your prop. Funny that, at the time, the package cost more than the pieces. It's usually the other way 'round.
As I've reported elsewhere I'm using a Hyperion 3013-14 brushless, 45 amp ESC and 3150 or 3850 LiPo. I get about 20 minutes on this setup, depending on how I fly it. I spent quite a bit more $$ than you did ( that was last spring) but I bought the stuff at 3D Hobby Shop, about 30 minutes away fron the house. I saw the same setup fly in a friend's SS-EP, duplicated it and am happy with it.
Over time, I spent a bundle on motors, batteries and ESCs. But I was playing around and having fun.
Cheers,
CR