Hi Andrew
I was fortunate to spend this weekend at Star Stuff where Bintel had a setup. I spent a good hour or two with them as I wanted to begin guiding too. Where I got to was ZWO 120MM (mono has 4x resolution) on a ZWO 60280 Guidescope and as others are suggesting with a 0.62 Lepus reducer. As you have an 11" you will also benefit from a reducer. As I interpreted it if you have too big a difference between your scope and your guidescope FL then effectively they "swing" about two different pivot points. By having them closer in FL then the guiding will be more accurate and your trails at the outer edges of your frame will be smaller.
If you are running a full sized camera frame then this will make it even more pronounced. As I have a 600D APS-C then this will be less of a problem for me.
I also bought a filter wheel so I can planetary image as I get reasonably good polar alignment. Hope this helps! Clear skies!
