'fast' necks are normally charachterised by the fact they are flat and thin, because aparantly its easier to play fast stuff better.
oh also the laquer on the back of the neck is very thin so it is not 'sticky' so ur hands will slide over the neck more smoothlt. its pretty easy to see if this is the case. look at the neck and if it looks wooden and is not shiny and varnished. it should feel smooth,
as to the types of whammy edge again is a brand. the higher the number the newer the version, and i assume better
um u could check the guitar out on the ibanez sight here http://www.ibanez.co.jp/world/country/frame_uk.html
im sure they explain it
another idea for metal guitars is esp, jackson, bc rich, scheter
im sure theres another i cant rmember.
anyways hope this helps
edit: also something u might want to look for in a guitar is a thru-neck construction. this will give better sustain and also allow better acces to the high frets.