Never did a test with blocks but have experimented with saddles; steel, brass, aluminium, titanium, string savers and string savers with an insert. Steel brightens the tone, brass makes it sweeter, string savers make it woody, titanium is like steel plus, string savers with the insert is like steel with just little bit of treble knocked off, aluminum has a nice zing to it. I've settled on either brass or string savers with the insert.
I don't think the block will have that much effect, but never experimented with it like Alex. Currently have zinc (I think) in my lone gotoh trem equiped guitar. Can't say I have an urge to change it though it has the string savers with the insert, which made it sound much nicer.
Like all things it will have an effect, but how much I dunno. :dontknow: