Let's do the math.
3 feet = 1 yard
300 feet = 100 yards
So an arrow that travels 300 FPS can travel 100 yards in 1 second. If you lose 5 FPS then you got an arrow that can travel 98.33 yards per second. First off, you shouldn't try to shoot an animal with a bow that is 95-100 yards away.
Now shooting only 30 yards away, an arrow traveling at 300FPS will get there in 0.3 seconds. That's fast. If you use a WB and lose 5 FPS shooting at 30 yards away, your arrow will get there in 0.305 seconds. Slightly slower right? Screw that, it's just as fast. Really, what's .005 seconds?
Basically, it is just as fast. The whole idea of losing 5 FPS is a bunch of crap. Get the WB if FPS is your only concern.
Utilize Technology---Scout from your computer desk.