A bigger mirror means more light gathering ability. Stars and deep sky sky objects are fait points of light a long way away... with a bigger mirror you'll see much more detail, or in the case of imaging, your images will go 'deeper' with a bigger mirror...
Check out this link, head 1/3 down the page on the right hand side, and click the M13 Comparison image... I hope this helps.
http://www.obsessiontelescopes.com/t...22UC/index.php
I also have a G11, and have been watching Paul's rolling review of the GSO 12" RC (non-CF version) with great interest. I think for the time being the 10" GSO RC (CF version) would be a great combo with the G11.
Good luck
