I'm using [link=http://www.cheapbatterypacks.com/main.asp?sid=627788&pgid=loosecells]CBP750AA[/link] cells for the ign since the can handle a 20 amp load and because the pack is only 2.1oz. I figure 750mah is plenty, especially when I will get all of the capacity due to the light current draw.

As far as the main batteries I am running a 5 cell HR-5/4FAUP 3200 NiMH pack, but it's heavy, 10oz. I didn't realize it would be that heavy when I ordered it, I was more looking at the size and very low internal resitance. One thing is for sure, the servos work very well with it. Since I spent a little bit of money on it I will probably try it with the gas engine, but if the airplane flys too heavy I can switch to a li-ion setup and loose 5 oz, but I don't know if it's worth the $80 to me.

That said, I would go for the 2500's since that is a bit more flying time for 1oz.