I posted this guide here quite awhile ago, can't find it here, but for a guide to goto mounts read:
http://www.astronomyonline.com.au/De...37&scope=posts
A C11 is 13Kg, so your options are EQ6, Sphinx just, CG5 just - both are right on the limit, so no accessories!
The EQ5 is out, as is the Meade.
The Vixen Sphinx has a Periodic error correction of +/- 11 arc seconds to the EQ6 +/-25!
If you're maxing out on a C9.25 I'd say the Sphinx, unfortunately on the C11 I'd say the EQ6 as there is too much weight with accessories to do astrophotography, which is what the Sphinx is perfectly suited to.