I'm using the stock GSO 8" f4 imaging newt (the non-CF version, with 10:1 focuser and 70mm secondary), together with a MPCC, EQ6, 80mm guidescope/QHY5 and a modded DSLR. Using a laser for collimation. The scope didn't require any modification and is fine for DSLR back focus right out of the box.
Its my first AP rig, and I only bought it in January. I've been very happy with the quality of my shots so far (and i have very dark skies and a modded camera which helps), but i still have a lot to learn and i'm miles away from reaching the limits of my off-the-shelf gear. The stock GSO 8" f4 gets the thumbs up from me.
http://astrobin.com/users/rmuhlack/
(all of my astrobin images were captured with the setup described above)