I waited for others to reply, because I'm sure there are others who have more experience in this matter. But there was a guy on the Seymour Duncan Forums who recorded his guitar before and after modified it. He tried large brass blocks, steel blocks, and titanium. He really liked the titanium, but I remember thinking that the brass sounded best. I did a quick search for the thread but I can't find it.
Edit: found the thread:
http://www.seymourduncan.com/forum/showthread.php?181881-The-great-Floyd-Rose-Big-Block-Shootout
