From a luminance point of view, those subs are not much longer than I've taken recently with my f/5.5 scope, taking into account the extra f-stop or so advantage...I was exposing for 150s.
The difference with the mono sensor is you'll need to take separate colour subs
But maybe from a resolution point of view the seeing just wasn't up to it that night? I've noticed that before with my 1100D even though it has the CFA, so I'd expect a mono sensor of the same resolution to notice it more readily. Of course, this is the same effect we notice when planetary imaging...you've just got to try it on the night and hope for the best.