The Med in August will be hot and the prices will be high.
If you have any flexibility, we've done a few legs when ships are being repositioned to spend the summer in the Greek Islands. A bit early/late in the season, but we've generally had great weather. Possibilities include Lisbon to Barcelona, Barcelona to Rome, Rome to Venice, and Venice to Athens in the spring (with a sprinkling of RTs thrown in.) And the reverse in the early fall. Prices tend to be quite attractive on these legs.