IMO, the little added acuracy of a full lenght rifle won't be enough to justify the lenght.
Batterie size capacity is a plus, but it can be done on a M4.
The biggest thing I see between the 2, is if you plan on doing real CQB (In buildings) or not.
I've done room clearing with a full size M16 ans it's very cumbersome.
Even playing in dense forested erea will have you struggle with a full lenght rifle. You'll have trouble tracking moving targets with all the branches in the way. Crawling is also more difficult with a long rifle.
If you like the long barel, I'd get a M16 style rifle with a M4 colapsible stock, or a bagpul type stock. You'l get a little less lenght, keept the long barel, and you can store the batteries in a An-Peq unit, wich will put a lot of weight on the front of the rifle.
I suggest you try both rifles before you buy. It's the best way to know.
Vérificateur d'âge: Terrebonne