Anyone have any mileage with a largish self-propelled mower that works
good on slopes? I'm looking for something that'll bag, but being able to
take off the bag and just fling the grass when I'm opening up new
territory would be nice.

Like one of the other guys (was it Karl?) said, an old 12 HP Gravely
walk behind would work. I used to mow some pretty steep slopes with
one of those. I had dual wheels on each side and a 40" deck. If the
steering brake isn't worn out, it works ok. The newer solution
probably would be a walk behind zero turn mower. The old Gravelys
were all gear driven with a differential between the two big drive
wheels. Once you had the dual wheels and anything wider than the 30"
mower on them, you really needed the steering brake attachment to make
them easier to use. Actually the old original 8 HP Gravelys with the
30" deck may do the job for you without dual wheels and they're very
maneuverable without a steering brake. Now I use a Grasshopper zero
turn for my 4A. The Gravely's been retired to winter snow blowing.

RWL