talk to your doctor about it.  possibly you might be able to slightly
increase the power of your contacts to improve your distance vision.
perhaps you have a slight bit of astigmatism that a toric lens would
help with.  your doctor has the best information.

yes-- at prescriptions that are at about -4.50D strength or higher it
is necessary to adjust contact lens power down slightly to account for
vertex distance.

when your eyeglass Rx is measured it can be measured precisely.
glasses can then be made to exactly match your needs.  however when
soft contact lenses are used the doctor must put you in the closest
available lens power because they are premanufactured to certain
parameters rather than custom made.  sometimes people notice the
difference.

==============

You make it sound as if he didn't do a proper examination.  I hope
that wasn't the case.  There's more to it than strength - you need to
have your cornea's curvature measured, so you know what range of base
curves you can use.

As someone else pointed out, astigmatism could be an issue, if your
glasses correct for it but your contacts don't.

However, if you don't have signifcant astigmatism, then you should
bump the contacts up to the next step (they're manufactured in 0.25
diopter increments).  A soft lens should have correction at least as
good as glasses (there are several optical benefits to being in
contact with the cornea, as opposed to being suspended a variable
distance away).

If you do have mild astigmatism, bumping might still help.  You can
also try aspheric lenses, which supposedly help with mild astigmatism
(i.e. less than 0.75, which is the minimum that toric contact lenses
are made to correct).