I appreciate the kind response. I don’t mean to come off as abrasive… Really. 
I can just get a bit passionate about this topic!
RE: Pinky
The reason I prefer pinky resting SOMEWHERE on the guitar is for proprioception (“seeing through feeling”). If it’s not touching the guitar and I need to play passages with ringing notes (EG: Carpe Diem section from A Change of Seasons / Dream Theater), then I still have some sense in space of where my hand is above the strings. When you float without any kind of something touching the guitar, you are required to activate many muscles in the pecs/lats, shoulders, and forearm to attempt to get stabilization… This leads into the “too long of a lever for accurate control” that I allude to in my motion video (Neuroscience of Picking).
I am never exerting any kind of “force” through my pinky. It’s hanging there limp. In fact, my JP15 has a glossy worn spot where my pinky has dragged along for years. Ha!
RE: Thumb
In my technique, specify that the thumb should only be used for one thing, and that is adjusting the pick ANGLE**. Not the pick slant. Many people preach a 45 degree slant. I find that a 45 degree slant is too fluffy. Flat is problematic because the pick doesn’t slice through the strings. My recommendation is to see a middle ground. (“22.5 degrees”)
While the pick, *pick grip strength, *pick depth, *pick angle all matter a ton… We should not discount the major impact that the Amp/IR combo you use can accentuate harsh articulation.
(* = These are the elements of a concept I call the Articulation Triangle)
Start experimenting with each of the aspects I listed above with no volume or an unadulterated clean tone. Find a combination of those that produces a desirable attack, then go to whatever sound you regularly play with.
On picks - I and many of my students find that the Flow style picks work well for my recommended hand setup. I especially like the Flow picks because they come in all different sizes. I prefer JP Flow 2.0 for “shred”. I use the 0.73 for cleans. I use Dunlop Jazz III XL Max Grip w/ the rock/country-ish band I play in. The Jazz III XL is a little steeper, which is great for more articulated parts w/ string skipping.
** - The only other place I use my thumb in technique is some final, slight adjustment when doing sweep picking to help maintain the angle…
(It also comes up in 1NPS stuff… But this is a totally different animal than sustained shred.)
RE: Middle finger
I recommend “stacking” the middle finger onto the index finger.
This is because when it hangs loose and you’re playing on low strings, it risks bumping top strings. This works for some players, but it takes effort. Sometimes, when I’m playing 7 string, sure… My middle finger does come off a little bit. I’m not a robot.
If you use the “fist” style grip, I find that for many players (myself included), the last joint of the middle finger sticks out bumping the strings. Players compensate in all kinds of ways:
- Floating the hands > poor string accuracy / not knowing where they are
- Rotating the wrist/arm upwards to get the joint off the strings > compromises muting
This CAN depend on individual hand geometry, but closing the fist entirely MAY compromise the availability of other motions.
A fist grip with the pick rest ON or past the last joint in the index finger also compromises a helpful degree of motion to be had with index finger+thumb movement… Again, only for slight final positioning of the pick and NOT the primary picking motion.
RE: Biomechanical optimization
I think anyone would be hard pressed to argue that any particular grip offers a particular advantage with the same degree of exactitude that one may argue any particular picking motion may provide a benefit…
This is because the grip is the final moment at which our hand interacts with the instrument. The instrument was not made for our hands. It was made for the strings!
So, unlike picking motion (which may be affected in a variety of ways), pick grip is a place where we must consider how to conform to the guitar not with “the best grip”, but one that offers the least amount of drawbacks.
Hope this clears things up! 