I think I prefer option2, as having a new event type for this aids
clarity.
Option 1 has two problems -
1. It's not obvious to programmers that a scrollwheel produces mouse
pressure
2. It relates scrollwheel movement to the mouse - which is not IMO a
good thing.
While the scrollwheel is located on the mouse, it really has little to
do
with it - the mouse being a tool for moving around a 2D environment,
and the
scrollwheel really being quite an artificial add-on, located on the
mouse
solely for physical convenience.
This is rather like the steering wheel on a car including the horn ...
the extra
control is convenient to put there, but has nothing to do with steering.