We usually use forward pitch on most conventional drillings where the span is much shorter. As Brickguy stated, your thumb will need good flexibility and the lateral measurement will play a very important role so you won't hang up upon delivery.
One of the pros of forward pitch would be the ability to have a feeling of superior grip through out the back swing, but if your span is not adjusted to accommodate the thumb pitch your fingers will pull back upon release causing you to clutch the ball.
One of the cons of forward pitch is hanging up because the thumb doesn't slip out as easy.
My suggestion would be to start out no more than 1/8 forward while decreasing your span accordingly to secure an equal match in the change, try this with a old ball if possible, and drill the thumb hole at least 1/64 larger than you generally use, you can always add tape if needed.
Also know you may have a tendency to loft the ball out a bit further until you get comfortable with this new grip.
I can not use forward pitch, it reaps havoc on my thumb, which is very stiff and rigid. I usually use 1/8 to 1/2 reverse but drill one size smaller on the thumb.
Hope this helps.
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