Hi Robbo
Due to the renewed intrest and crowds at Moto GP, unless you like sitting in traffic jams on the way out, suggest you take the bike. Although it must be about 400 miles return from Pompey, which makes it a long day unless you have a very comfortable bike. Our return trip is 250 miles and I get home knackered, although my bikes not designed for touring, I'm getting old and we don't use any motorways. Van with bikes in the back for the last 20 miles prehaps?
Beware the A5 around Northampton, on bike race days the police make Himmler look like your favorite auntie.