Question for the CCD gurus

I am in the market for a CCD-equipped telescope to do minor planet
astrometry.

A strict requirement for astrometry is an image scale of less than 2"/
pixel and the setup should be able to image objects with a limiting
magnitude of at least 18.

It should include a GOTO tracking mount and cost less than US$6500.

I have two combinations in mind:

- an 11" SCT on a CGEM mount using the HyperStar lens and a SBIG
ST-8300 CCD operating at f/2 - no guiding required.

- a 9.25 SCT also on a CGEM mount but with an autoguiding SBIG ST-9XE
CCD at f/10. I could use a focal reducer to shorten exposure times
and to increase the field of view.

Any suggestions?