Just to prove that good does not always need to be expensive, some of us have been using the Turnigy series Lipo batteries for ultimate performance. They seem to be on par with latest offerings (45C and 65C) from Thunder Power. You will find more information on forums like RC Groups but suffice it to say that the following cells / packs are very good.
Turnigy 6S 3000mah 30C, 35C and 40C.
The Turnigy 6s 30c 3000 packs have proven to be very good and have a long life, The 35c 3000’s of the same type have proven to be even better as far as performance goes which can only be measured as voltage under load.
The latest Turnigy Nanotechs truly do pack a punch but only the latest 65c-130c or A-specs. The life of these packs still remains to be seen.
For your first year, you can use a Turnigy 4S 3000mah with the HK-200 speed controller. This will deliver enough current where as the bigger 5000mah cells may not fit your plane as they are slightly wider. Ultimately you will have to combine the parts as you see fit and to fit your model.
Try to avoid using odd cell number Turnigy packs as they have a Z link on a piece of PCB that will melt at higher currents. Thunder Power packs do not have this problem.
In winter it is essential that the battery pack does not start from to cold a temperature. For this purpose most of us tend to heat the battery pack up before the flight in a home made heater of some sorts.