With the riding that you're describing whatever bke you get (Commie or otherwise) you will be compromised to some extent at one end of the scale or the other.
Depends where you want to be compromised.
If mostly XC then a 5.5 for sure.
If you do some DH riding and are considering the Mega then perhaps a 5.5 VIP frame build where you could choose burlier components - stronger wheels, tyres, double and bashguard etc., or you could get one of the stock models and upgrade parts later for the Mega.
And just so you know exactly where Tim stands, he's talking about (or already done ?) swapping his Meta 666 for a MiniDH for the rough stuff
and getting a hardtail for his XC riding. He's having trouble keeping up with his mates on their hardtails
