While you may notice a bit more recoil it will still be mild. The biggest drawback to me is that the light rifle is less steady from any feild position, and body tremor or 'wobble' has less mass to slow that 'wobble' down. A heavy rifle sort of "hangs there in space" and you get your wobbly ass behind it. (that's the theory anyway). Try shooting a 12 to 15 pound sniper rifle and you will see what I mean, they just WANT to shoot steady.
Of course the advantage of the light rifle is that it is easier to carry. Original A1 Rifles weighted about 6 pounds, now with heavy barrels, lights, fancy rails, lasers, optics, you name it hanging on rifles they can easily top 10 pounds for a field rifle. I like them light and simple myself, but you need at least one tricked out AR too!