Hey Kana,
I have had both the 80ED & 120ED on a NEQ6 (with my friend using the 120ED on a HEQ5). It is a *brilliant* set up and you will get some amazing images them. Astrobin has plenty of images taken from these scopes which will give you a taste, otherwise if you look at some of my older image uploads you will see what an amateur like me (or more like a first timer compared to folks around here) can achieve.
If I had to start again or stick with only one set up I would probably buy a 120ED second hand and a NEQ6 (or a HEQ5, both can handle the weight fine) second hand, and use a OAG. I personally would go 120ED as it gets a bit closer to the action and with a simple reducer, you can have similar FOV as a 80ED as well. In fact I have images using a 0.67x reducer with the 120ED which shows how well this works. The only merit for the 80ED is that it's cheaper, comes up more often second and would be slightly more forgiving with tracking errors (as it's got 30% 'less zoom' than a 120ED).
Dont be afraid to pull the trigger on any of these second hand here, all the sellers are great and I found the members to be very helpful. Worst case you can always sell your equipment here and try something different
I should know, I've bought and sold many times trying to find the right set up for me!