I haven't got the E-Flight Extra but as nobody else has replied thought I'd at least try and help. I've 2 other similar planes I fly on 2170's, both are about the 34oz level so 5 / 6 oz's heavier tah teh E-Flight and both using slightly more powerful engines so probably drawing a bit more. I get easily 10 minutes and could probably stretch it to 12 but I'd rather land with a bit left in the pack than crash / deadstick 500 feet away and it's pot pluck to see how you're comning down.
My batteries are quite oldish now as well and could probably do with being changed, as a guestimate I'd say you'll get 12 / 14 mins out of a new pack with throttle management and maybe a bit more.
Personally I wouldn't go to the larger ones as it may fly like a pig and will increase the wing loading although if you're only going to fly sport and not 3D then you may get away with the 3000's but I wouldn't buy 4 straight off but at least try it 1st, bear in mind their recommended is in the 1320 - 2100 so you're already at the top of their range !!!!!!
Hope that's of some help.