Like chris has already said, the difference of a 10 to a 8 is a bit noticeable. back when i first started i had my 10" and a friend had his 8" both skywatcher dobsonians mounted up on EQ6pro german equatorial mounts GEM's using a 20mm Meade series 5000 eye piece the difference was the images where brighter, and being brighter meant that i could appreciably see more in galaxies, faint nebula. Also chirs is right with saying that a 8" in the country will preform like a 10" in the city. but a 10" i the country will take some big bounds on a 8 in the country!
The flame nebula is a good one to test out on, as its right on the edge of visibility with these scopes, In my 10" i can see it pretty good, where as the 8" i am struggling.
As for the difference between saxon and skywatcher, its like skywatchers poor brother. Not that they are bad.... but they are not made exactly the same. I would rank GSO and Saxon on the same level with the SW slightly ahead. at the end of the day its just the difference in build quality as the mirrors are on par. I could go into information over load for you but its counter productive. I wouldn't be swayed either buy all the extra goodies they throw at you, as most will tell you the kit that you get with the scope is great for the first 6 months until you get your feet wet, then you will upgrade your eye pieces to suite your viewing pleasures. high mag, wide fields, multi element eye pieces and the like.
Good luck and don't be afraid to ask many questions
oh and welcome to the forum
Brendan