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.