I think f10 is better for visual observing:
- with f6.3 the central obstruction
is greater and less light will come to the
most valuable central part of your eye.
- you won't have a larger or brighter field
of view with f6.3
(Bear in mind that the exit light
beam (sorry, dont know the correct English
word for this) should fit into your eye
when there is a central obstruction).

When you do astrophotography with f10 you
can use a focal reducer. Reducing too much will
deteriorate the outer part of your picture,
but I think this will not matter very much
with a CCD, because the CCD is so small.

I have made my decision for 10" f10 and I am
very happy with it, but I have made no pictures yet.