The FSR Riser is the easiest way that I've found to shoot First Strikes effectively at range.
The sight you put on the FSR is up to you.
I've noticed red dots were easier to see where the shot went over using a x4 or whatever scope. It was also easier to see if I actually hit the target when using a 3-9 scope, but couldn't tell where my shots were going if I was way off.
If I had a spotter per say I'd go with a 3-9 scope. Running solo like I tend to do on missions I go with a red dot.