I have the carbon fibre RC8 and at one point did have a Tak FS60 riding on the top with similar intentions.
The thing with the RC8 though is that it is heavy at the back and it comes with this huge amount of back focus (240mm give or take) in the form of extension rings which whilst its great for putting things in the imaging train it does mean that balance is fun. Start adding STL CCD's and filter wheels and it's an absolute hoot. I added a set of losmandy counter weights originally on the rail on the ota at the front to balance then relocated them to an extra long mount saddle at the front so there was no addition force on the OTA itself.
I was never really happy with using the little apo for guiding at the 1600 fl. There were still guiding issues and undoubtedly some flexure problems so I went with an OAG and because I wasn't using the TAK much, took it off. It's just unnecessary weight if not used which again has to be balanced across multiple axies and in an effort to get everything just so and simplify things, I stripped the rig down to only what I need to image at the native focal length. (I had the reducer as well but never used it as I like the FOV as it is) If I want to do widefield, it's straight forward to put the Tak back on and guiding is still covered by the OAG setup.
This works well for me personally. I couldn't tell you if the OTA was affected by the additional scope and the extra weights you need but I went with an approach of eliminating any possible causes of problems across the setup rather than point fixes and as a result my data is that much better.
The RC8 is great little scope. My one holds focus incredibly well (carbon fibre tube but an after market focuser was also added...),is quick to cool down, the OAG is awesome and I am getting good data with it. just a pity I am not that smart at processing..ho hum.
