Thanks for your reply. Did you actually try the 8″ or did you figure it would be too big / not inexpensive for you?

Yes, I did. I tried Oukitel RT3 (8″). It is also very cheap, so price wasn’t deal breaker. It was way too big for me, cluttering my clear view to instrument cluster and to road, too. Please note that this is only one guy’s opinion and try for yourself. Either borrow one 8″ device, or simply make paper template in real dimensions.