hi Stefan,
no worries; you have a mount that could hold up to about 10" newt (f4). I can't comment on refractors as I don't have one, the ED80s get a good wrap though.
If you do decide to go a newt i'd suggest an 8" f5 its fast and a lot more forgiving than f4. its also pretty cheap which means you can pump money into a quality focuser - that is very important when imaging. eg
http://focuser.com/products.php it also has a nice field of view. if you were happy with a stock focuser you could also spend more and get a carbon fibre tubed variety.
I'll let others comment on the refractor options. however it may be worth visiting an astro society to compare side by side.
cheers
russ