That being the case, you have both a beautiful deep sky image image and significant solar system object capture. Is there anyway to use the planetarium SW to predict when such cluster events will happen? I would like to try a capture.
I would just use your planetarium program of of choice with a large asteroid database loaded. I would figure out how deep you can go and limit it to show only brighter objects. Keep in mind that these are moving so while you might be able to get to 20th mag on a star, it could be 17 on slower-moving asteroids or comets. At this point, if you look in the 'asteroid zone', I'm sure you'll find numerous opportunities on a nightly basis. I tend to do this kind of thing when the moon is getting brighter and I can point somewhere opposite.
Here's what TSX looks like for my FoV tonight. I just pulled up the galaxy mentioned above and moved around a bit.
I would add that one of my reasons for liking TSX for this kind of thing is that it gives Ra/Dec movement rates. I'm sure others do something similar. I can use these numbers along with my arcsec/pixel ratio to determine how long I can expose before I see trailing. Think having a 17th magnitude asteroid going by earth. That can be captured from the city with my refractor or so it seems. Once I figure out that it will trail in a couple seconds, capturing isn't so easy.