Hi Steve,
I have a Saxon 10" pusher and a 14" sky watcher goto. The 10" I chose first ( after exhaustive research) with a 14 as a close second but ultimately rejected option.
My 14"goto followed about a year later when an opportunity came up to buy one new whereby someone else had ordered and paid the deposit and then bailed. I only had to pay the balance. Armed with spousal permission a deal was struck. But I digress.
Everything has a pro and a con, and the 14 goto has heaps on both sides of the ledger. The short version is: cons are mainly to do with logistics the pros are mainly to do with the seeing.
For more detail, please see below. So here goes:
1) the 8 or 10 pusher should always come first and you should keep it after you get a bigger goto dob. You learn the sky much better with a pusher, goto makes you lazy. I have regressed in star knowledge since getting mine. I'm making a conscious effort to use the 10" regularly these days. You tick this box, so move on.
2) yes in pictures the bases all look similar but they are all scaled up with each step up in aperture. Further to this point, the base of the 14 is in fact a good deal bigger than the 10", and the alt/az motors mean a massive amount heavier. The 14 is the smallest where the base can be unscrewed into 4 pieces. This is vital to an urban dweller like me who makes dark sky trips for seeing deep sky objects. But also needed domestically because with out some form of trolley even just for moving it around your own property it is too big for one person alone. For moving it around the backyard I had a dolly welded up recently so I will be able to keep it all assembled, cables and all, while at home. Please see picture. Up to know I had the ritual of disassembly and piece by piece movement just to shift it 20m from my study to the garden dark spot. A laborious process!
Ok, that's pretty much all the negatives out of the way.
3) the views in the 10" are fantastic, and the 14 is simply mind blowing!
I've looked through a 16" as well. Not as big an improvement in seeing from the 14 as the 14 was from the 10, but still better, no doubt about it. Aperture wins every time!
Deep sky objects come alive in the 14". If you are into galaxy structure, which I am, you will love it. My brother in law is a constant companion on dark sky trips. One time he described the Grus Quartet as 4 "bright galaxies" To a friend in an email or something. His correspondent replied he had never heard anyone describe the Grus quartet as "bright". Admittedly in the 10" those galaxies are just smudges.
4) views of the planets are more detailed than in the 10" but demand a different discipline when observing. Atmospheric disturbance is a definite factor in the 14", and you can't really get away from it. But if you are willing to accept that within a 30 second window you'll have 5-10 seconds of excellent seeing, those 5-10 seconds are awesome! The detail is amazing. The GRS is positively bright in the 14" and my favourite part is the wake in the southern equatorial band left behind by the GRS. The eddies and vortices that trail behind it are mesmerizing. Last week, the BiL and I watched the double transit of Jupiter in both the 10 and 14 side be side. Interesting comparison. The view in the 10 is more consistent but does not give the same highs as the 14.
5) goto function is reasonably accurate when you search for objects and tracks very well once you have found and centred your target. I find that the goto is usually out by up to 1 degree when you first seek a target, so a low powered wide field eyepiece helps. But I also find that the error is consistent through the night. Once you get used to it, you'll know where to always look.
6) The tracking function is great when sharing the viewing with others. This is one of its best points. Everyone gets as many turns as they want, you don't have to keep re-centring between each viewer. Swap eyepieces, filters, go make a cup of tea, no worries it will hold it. I've done all of these, I'm not exaggerating this point one bit. I don't think the tracking is accurate enough for astro photography. But I'm no expert there. For visual kit is perfect.
7) it does the dob nudge with far more subtlety than you or I can achieve. Again a great benefit for viewing at high power as the view settles quickly after every movement. I find this a huge bonus for planets and planetary nebula.
8) I'm 185cm tall, the 14" is the ergonomic choice for people around my height. I can break my back stooping over the 10" and needed a step ladder for the very top of the 16" altitude range. The 14" is just right for me.
One last point, and this can be either a pro or a con. These are fast scopes, so demand higher quality eyepieces. And once down the premium EP path you go, forever will it rule your observing destiny! Even with your smaller telescopes.
For me aperture wins every time, but a 14" goto is not a beginner scope. You need time to learn its quirks and to get used to it. But if you are patient and keep at it, it will reveal wonders. I'm very happy with mine because of the things I've seen through it and who I've been able to share it with.
Anyway, that's enough verbal diarrhea from me. Feel free to get in touch if you have more detailed questions.
Good luck.
Adam