Thank you.
I think (1 3 4) for whole/whole has the benefit of simplifying the fingering sequences of some of the patterns that Paul plays, and that it often helps to reduce the feeling of position shifting during those patterns.
However, I think that Paul is unusually suited to that combination, and most players would be better suited to (1 2 4) for whole/whole in almost all instances, which I believe is a significantly less expensive combination.
Paul Gilbert is about 6’4" and he has a huge hand span. His 4th fingers in particular are very long, and the difference between the lengths of his 3rd and 4th fingers is relatively small. Paul is able to use the (1 3 4) combination for whole/whole over the length of the neck without it requiring an unnatural posture of the fretting hand. He also picks a lot of notes and doesn’t really play much legato.
For me personally, (1 3 4) for whole/whole is much more difficult. My hands are roughly average in size. I have a respectable hand span, but it’s mostly the result of flexibility and range of motion. My fingers are maybe a little longer than average, but my 4th fingers are quite short and my 3rd fingers are proportionally much longer.
For most of the neck, the lower frets in particular, the (1 3 4) combination for whole/whole is just unworkable for me. It forces me to keep the ring finger very curled and the 4th very extended, which is uncomfortable, and further increases the difficulty of that combination for me. I can’t comfortably maintain the fretting posture required, and my ability to hammer and pull-off with that combination is significantly worse than the (1 2 4) combination.
I could potentially use that combination for whole/whole higher in the neck, and I sometimes do, though more usually I would reserve (1 3 4) for minor third and whole tone. Even then, I usually prefer (1 2 4) for minor 3rd and whole tone over most of the neck. To use (1 3 4) for whole/whole higher in the neck and (1 2 4) lower in the neck would require me to learn multiple fingering sequences for different shapes, so there really isn’t any benefit for me, especially since (1 2 4) is comfortable for the entire range.