Difference at the upper ranges of weight are minimal. I've noticed a very minor difference between .43s and .48s at the longer ranges (70m+), and basically no difference between .45s and ,48s. I'm sure there is a difference between .45s and .48s, it's just negligible in practical terms.
However, I would advise against grey BBs.
In theory, they're amazing, since the enemy won't see them coming and you won't get those annoying shots where the enemy sees the BB at the last second and dodges out of the way.
In reality, you also won't see where they're going, which means you can't make adjustments based on weather or other conditions; airsoft guns are not precision rifles. You can perfectly zero your airsoft gun so that you're hitting where you're aiming, but then you go out into the game and the wind is even slightly different and now you're convinced that player over there isn't taking his hits, when in reality your shots are going 5m wide because Mother Nature decided it would be so, but you have no idea because you're losing track of them at about 40m before the wind is carrying them off to the side.
I tried grey BBs, I hated it.
