Re: How fast can you shred?
I can only go as fast as 11nps for alternate picking, and about 13nps for sweep picking.
One thing that I have noticed when practicing for speed, your phrasing will suffer unless you also practice licks and stuff.
A friend of mine once told me this: "You can shred as fast as 30 notes per second, but if it didn't sound great (e.g. bad tone, phrasing, note choice, etc.) nobody would even take a second look (or listen) at you." You see, guitar playing isn't a sport, and while speed can be really cool for some, it isn't necessarily the end-all and be-all of great guitar technique.
I'm not an actual believer of soul per se, but I do believe that guitar playing should be able to excite a reaction from audience, not simply through raw speed and technique.
This was how I was drawn to guitar playing in the first place. I listened to a couple of players and felt moved by their playing somewhat (y'know the staples: Hendrix, Clapton, Van Halen, etc.) and this feeling their playing gave me inspired me to pick up the instrument myself.