Ok so I did some testing and found some interesting results.
Player stream distance is set to the standard distance of 400, as is the SA-MP default value. It cannot be set higher. That being said, draw distance comes into play. I cannot see a player past about 150 with maxed out draw distance. That being said, when I aim down a sniper rifle scope, I can see players up to 400 units away. The problem is, they can't see me. I don't want to create a situation where you can't see who is shooting you. They aren't even that far away.
Some screenshots for illustration...
This is the limit of where I can see James, at about 150 units:

Any further back, he's gone:
NOTE: This is based on camera position and not player position.However, even at up to 400 units, I can see him in the Sniper scope:

But slightly further back, not so:

So to conclude, yes, the maximum range of the Sniper could be 400 units, and the victim does get hit correctly, but they cannot see the shooter, which I think is a problem. People would be livid at dying from someone they can't even see. The maximum range is currently 200, which is actually higher than the 150 visibility range already.
This is probably even worse for players that don't have max draw distance.