they vary in length, width and also the thickness and shape of the neck as well as the curve of the fret board.
usually ibanezzes have quite flat wide fretboards. and quite thin necks.
most people find the more curved the fretboard the more comfortable, but many people also say you can be more acurate with a flat neck. playing chords which involve the thumb over the top might be a bit harder due to the width.
but as you are goin for metal u wont really need em as u will be playin mostly power chords.
if you have quite wide fingers tyhe width will be good. if you have short fingers then u might find the width a bit of a problem.
but all this said, nothin certain. you might feell the oposite about the shape of neck after some experience, cos i dont have your hands and arms i can only draw generalisations.
as you are new to guitar you wont have a preferance of guitar neck shape. i would suggest playin lots of different guitars to check wat u like the feel of. but if u are a complete beginer they will probably all seem hard to play.
only other thing to consider is, does ur rg come with a whammy bar. if u are gonna use the whammy its worth it. if u will hardly ever use it it is better not to have one as it will be more convinient for changin strings, a bit cheaper, and will give ur guitar slightly better sustain. (how long the notes last)