The best ride outs i've been on are when there is a specific route of about 50-70 miles with lunch in the middle. This can be comfortably done over a few hours including lunch.
Also, its probably a good idea to drop the location which is central which nobody has ever been to before! and go for somewhere which somebody knows really well, and can plan a route for it.
The usual suspects for me would be Derbyshire, Yorkshire Dales, Central/North Wales. Sure theres plenty more...