Hi Tony
You have done very well ...good on you.
I have a guide setup but dont use in more than not because something so often plays up ...as a result I goto short exposures and trust me just do the same overall exposure using shorter exposures and you get the job done...the star movement means with short exposures you will get "automatic" dithering
for a start, ( which means drizzle can be employed ( which I believe does wonders and worth the longer stacking time)..also you wont hesitate to throw out a poor capture ( perhaps one of the most important steps I have found) and I think there may be a benefit from the noise point of view.
I am about to get a RASA 11 and my plan is to go for the shortest exposure it can handle which may be around 10 seconds to really push the short exposure approach and really minimise atmospheric movement.
Anyways lets not overlook all that you have done right as that is what you need to focus on and remember most folk dont notice if the stars are a little oval like...
Again good work.
Alex