well the ribcraft 585 looks a superb boat so i doubt you can go far wrong with one of those.
the ribcraft will be a slightly softer ride by all accounts. the osprey will be a heavier build and a softer ride still than either the solent or the ribcraft and will ride slightly different and seem more planted i suspect.
but as everyone will say, they are all good boats and depends what sort of ride you want
If you can stretch your budget to a 6.5 that would be good but go for the biggest engine you can, min suz 140 but perhaps a 150 budget allowing.
will be worth it for the grin factor.