when we did it we did Darlington-Hull, grabbed a pub lunch in hull on the evening.
overnight ferry hull - rotterdam (leaves around 7, gets into rotterdam around 8am), few beers on the ferry
rotterdam to nurburg (took till about 12 with a few stops for petrol and macdonalds breakfasts etc.)
two days at the ring
back to rotterdam, night out in rotterdam, hen spent the next day walking around a zoo hungover to kill the day (was actually quite good, was huge, everyone enjoyed it, but of a weird end to a weekend of cars, steak, booze and birds but hey ho...)
overnight ferry home to hull (left rotterdam around 8pm and got to hull around 8am)
then drove home from hull
in my opinion best way, ferrys always a laugh, same ferrys that go to amsterdam so have little "nightclubs" and casinos and people wanting to get pissed on so always good for a few drinks, just dont get too carried away and have a skin full.... plaine would be quicker, but more expensive and in my opinion more boring..