I would recomend at least three packs for a heavyweight. 4.4Ah is pushing it.
Note that to balance a 10 cell pack with the Xtrema charger, you need the charger, two balancers and the Balancer Interface Module.
The FMA Cellpro 10S does it all in one box: http://www.aurorra.co.uk/aurv2/productDetails.php?id=11
Personally I still prefer the MegaPower Infinity 960SR, because it graphically shows you the balance - you can see how bad the balance is and you can turn down the current if they are badly out, to give the balancer time to work. Seems to be tricky to get in this country though.