[QUOTE=astro744;583603]. An 8" f6 will likely have a 2" focuser whereas a 6" f8 may only have 1.25" (2" can be added though not always easily). A 2" focuser will allow much wider true fields with long focal length 2" eyepieces, but with an f6 telescope these eyepieces will need to be highly corrected ones such as Tele Vue or you will see abberations towards the edge of field.
Ben!
Just a correction to the above quote: The 6" does have the 2" crayford focuser, and I do use 2" eyepieces on it.
I have a 6" Saxon Dob and I love it to pieces! I'm a bit of a fly weight, but I can just carry this unit in whole for a tiny bit (though I put wheels on it). The 6" in itself does take up a lot of room in the car. I have a big boot and the base does not fit into it.
From much research I did not so long ago, I agree with others here... you would upgrade from a 6" to a 10", or an 8" to a 12". I love the fact with my 6" I can take it out on a whim whenever I want as it's fairly easy to move around. So, I use it lots! You will be amazed at what you see out of the 6". The larger you go though, the more the atmosphere mucks up your seeing; bigger appertures can show this up much more easily.. I barely comes across bad seeing on planets when I look thru my 6".