I personaly don't like the idea of anything touching the arrow during the shot so as such I haven't shot a WB and I can't offer any first hand evidence.    
I've heard its 3-5 fps on most setups.  Have also heard horror stories of shoting em in cold weather.  Wiskers get stiff/icy and accuracy speed go to hell.  Watched my buddy's WB have a big chunk break out of it when he took a spill and his bow went flying.  
IMHO spend an extra $ and get a all metal fall away.  Not a lot of $ when you're looking at the overall investment in your setup.  Save some money somewhere else.  Plus, the realiability, performance, and piece of mind are more than worth it.