I'm planning to build a guitar soon too, and i've been doing some research, and this is what i've found out about finger boards (there's not much on the sounds, you'll have to ask someone else about that), All i know is that Ebony and rose wood give a warmer tone, and maple gives a brighter tone, I dont know about Cocobolo's sound...
Here goes!...
Ebony: the heaviest of the hard woods, is very dense and machines well, and resists warping and cracking. It's popular for finger boards due to its stability and strength. It hold fretts extremly well, and has a striking appearance, but it is expensive (Pau Ferro has bee reported to cause some allergic reactions, just to let you know, but dont think that plank of Pau Ferro is gonna jump up and kill you. I wouldn't worry about it too much)...
Maple: Strong, very heavy, which is light "blonde" colour. Maple finishes well. It is advisable to laminate the neck from two or three peices for increase stability. (sounds bright, hendrix_jimi said)....
Rosewood: like ebony is a popular choice for fingerboards. Rosewood is oilier than ebony though, which makes finishing more difficult. Brazilian rose wood is more sought after, so it's more expensive (yes, i know, it's all the fault of these capatalist pig-dogs, lol :)), so indian rose wood is sometimes used as a replacemet (I don't actaully know what difference is between the two)...
Cocobolo: I can't say enough wonderful things about this wood. Once seasoned it's very stable and IMHO the best frett less finger board i've seen. I've seen some that are several years old and they have less chatter lines on them than brand new fenders out of the box! No joke... Oh yeah COCOCOCObolololobo is known to be toxic, so for god sake dont chew it!!!!... like you needed telling.
I thought that making your own guitar is alot cheaper, it's not as cheap as i though it was!
About "fastest" wood, hmm, i though what fretts you use really make the differnce...
Hope this helps..