I have also arranged for a transfer by Sorrento Limo to Positano (from Rome) in Early May with a "free stop". Having been to Pompei two years ago we'll opt for a short stop at either Herculleaum or more likely Mt Vesuvius; will report back in about three weeks.

I think it also depends on when you are going. If it is in the summer and very hot out, you may only be able to stand about 2 hours in Pompeii. There is NO shade. You are really out in the rubble baking like a codfish, beached on the sand.

I should of mentioned, I'm leaving May 14th.