We did Portsmouth to Bilbao with P&O. Smooth two night crossing there, one night force 10 gale crossing on way back - not for the faint hearted :)
The drive from Bilbao to Condado lasted from 8am til 5.30pm with a 30 minute break and a couple of stops to swap over the driving. We spent approx 30-40 euros on toll roads (one way). Reasonably straight forward drive - we did'nt get lost (did use satnav & map) and the toll roads are lovely and quiet (bit sticky around Madrid though).
The ferry was an experience - we both agreed that we would do it again but only if we have 4/5+ weeks as the whole trip took 6 days out of our holiday. There are plenty of facilities (as well as a strange mix of people - some on mini cruises costing £35) onboard the Pride of Bilbao. On the way back we stayed at the Novotel in Bilbao the night before as the ferry left in the morning - we did'nt want to miss it!
Hope this helps, we are away at Condado now for a week but if you have any other questions drop me a line in the New Year.
Louise & Rob