Nope, not as far as I've found out. Due to the incredible differences in mag and size and conditions, filter required or not, you name it, there are no definitive rules.
But !! What I have been doing lately is taking consistent notes and numbers down of all imaging sessions, Drew up an excel Spreadsheet with boxes for almost every conceivable piece of data and from that I am getting better results as I can reference back to what worked and translate it to new targets. I also have a programmed test sequence that can be run first, increasing exposures to find the optimal starting point if necessary.
A good starting point is to get 'Imaging the Southern Sky'. It identifies, images and gives basic stats on what was used. The writers used a specific setup but from that you can work out what is possible within your own setup and location and get some idea of the exposures times and setup required. Having got my own system working reasonably well now it is giving me new targets and numbers to try.
With the 102mm ED Lunt, the 450D @ ISO 1600, my start point is a 20 or 30 sec exposure which confirms target , focus etc and I work from there. Last night 60-90 secs was the optimal point.
BTW: I don't see too much wrong with your image, better than I've acheived so far.
As I said there is no definitive rules but once you have a stable setup you can write your own to suit. The data recording is critical.
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