Here is my first try at electric.
Tell us the airplane weight. The first crucial factor is whether it's generally a stunt plane (it is). The
next crucial factor is
how much does it weigh.
You've got to be spinning that prop at way more than 7000 RPM, or I'm cracked. Did you tach the prop, or is that 7000 number what the program is set to? You didn't say if the system is speed regulated -- does the timer regulate the speed? (Edit -- no it doesn't -- there'd be an extra wire in there if it did) If not, then you need to use an ESC that has a helicopter mode, and set it up to use it.
A 4-cell 2200mAh pack should be enough to finish a six minute flight
at normal speeds for a 36-ounce stunter. A 46-ounce stunter should be right at zero battery after a normal flight. You're going way faster, so the thing is going to use power quicker -- this'll both heat up the motor and drain the battery faster.
If your stunter is heavier than 36 ounces, you just need more battery. So, tell us how much it weighs, and we'll give you some guidance.
In the mean time, I'd cut the speed setting to 2/3 the current value, then fly again and time the laps. You may want to "short tank" the thing (set it up for one or two minutes of flight time) until you have the speed sorted out. I'd go for lap times a bit over 5 seconds at first (between 5.2 and 5.3, at a guess). Once you get there, then if the plane is no more than 42 ounces, you can try full-length flights. You'll be beating up the batteries (for long battery life you don't want to use the full rated capacity), but you'll at least be flying.
After you get the speed correct, see how much charge you're taking from the batteries for a full-length flight, and use that to determine the batteries you should get next. Take the mAh that your charger puts into the batteries, multiply it by 1.25, and buy a 4S pack with at least that much capacity.