Pull-off when play fast!

Well is known that there is a specific technigue to perform a legato movement with your left hand...I'm curious to know if i have to keep this technique as it is when i play fast phrases!:I mean to not pull off the string but to just make the movement of my fingers..and with the little help of my marsall to hear what i want to hear !Is that right or i have to try harder for a better teqhnique...For example i know that Iron maiden solos are supported very well from the amps...and not from Dave Murrey technique as other guitarists...

The word for speed is economy. If you want to play faster, your movements have to be as powerful, but with less motion.
When you see speed devils on http://www.chopsfromhell.com those guys barely move their right hand, and their fingers lift so little from the keyboard that you barely see them moving.
Of course, the compression given by your amp helps playing legato phrases with less effort.
Study Allan HOLDSWORTH for legato, the guy inspired Satriani.