I am playing on a 1 3/4 nut width, standard thin full scallop 16inch radius "shred" neck right now.
I have large hands, my pointer to pinky stretch is comfortable from first to 8th fret on a strat style neck.
Also I am originally a classical guitar player so I figured I should go with the wide nut due to those two factors.
After playing on it I have decided it's NOT that good for fast riffs and leads.
Although its great for finger picking on the electric.
Here is what I don't like about it.
1) like dan025 said, the string fall off the side of the fretboard way to easy, and if you have stainless frets like this neck does its even worse becuase the strings slide much easier when bending and doing vibrato.
2) Its defiantly slower doing arpeggios and string skipping licks and even a little slower crossing strings with scales.The slight string spread makes a difference you can defiantly feel.
3) usually when I play leads and am sustaining a note I am using the side of my fretting finger to mute the neighboring strings so they dont ring or bleed.
Its a little harder to do with the wider string gaps.
I went through my whole guitar collection and played on all the necks to see what one felt the fastest. I also went to Guitar Center and played on a ton of guitars and brought calipers to measure the necks on the ones i liked.
All the killer fast guitars that were great for lead had a narrow nut 43mm or 1 5/8 inches.
Flatter radius, mostly 14 - 16
Stainless steel frets bend easy and feel really smooth, way better in my opinion
The fastest neck shape was the thinner back profile for sure.
And set up is real important to, obviously low action helps a lot.
Of course this is only my experience and you should play on as many guitars as you can and find the feel you like.