Wow we are in the same dilemma ill try to search for the ics cansofts for availability. I havent had much luck in finding src gen 3 reviews aside from the seller and the guys who just got hold of em and have an awesome moment with his new purchase.
I am not AV but back where i came from i have all ics setup. 2006 limitd edition full metal ics and a m4 ras ics. They are pretty good aegs really easy to work on. And yeah i have 2 spare upper gearboxes for different springs with different barrel lengths and mock suppressors. They are pretty customizable on that regard plus dont forget the little things like a good motor a strong gearbox( stronger than a v3) and a spring relax function.