My opinion only.

I would rather run dual 2100's than one 3300 or 4400. I run dual batts on all big planes just for redundancy and safety. Price is abou the same. Dual switched plugged right into the AR7000. ONe inthe battery slot, one in any open slot. see my pic

Now that said, my recommendation is to go to Troybuilt models website and use their Lithium Ion batteries that they sell if you want to use a regulated system. I would recommend miracle switches in that setup. OR if you havent made the investment, you can use A123 M1 Lion batteries without a regulator. read up on them. they require a special charger, but I like them alot. they are 3.3 volts per cell instead of 3.7 nominal.

Why: you can scale up to larger plane with same setup.You can use the same charger. I am not a fan of LIPO's on a plane like this.

I am not a fan at all of the 645 servos, so if you haven't bought them, I would recommend something else. the 5955 is a great servo. 5985 is a great servo, JR821 is a good servo for sport. I personally prefer coreless motor servos, they are more crisp. my opinion though. I have 635's and 645' on a plane and they dont center well and are slow to me. JR8411's are also great, they were the standard not long ago.

http://www.troybuiltmodels.com/Servos.htm go here and study. then go to JR-radios.com and look there too. I try to remain upwardly mobile on servos. my personal preference is 5955's and 8611A's. I use them on everything large. I know its over kill but they friggin work, and theyare fast and strong. A 73 inch plane can use smaller servos though Im concerned about flutter on 645's. I think there are better choices. by the way, TBM has about the best prices on gear.

good luck.