Cunard has the most regular crossings. The other lines are largely seasonal and run eastbound in March-June typically and westbound August-December. There are some bargains to be had within the 75-90 day window as they're not popular with typical cruisers. The typical southern Florida to Lisbon leg is usually 8 sea days + 1 day in the Azores, Canaries or wherever.

Seabourn has repos too of 9 days (Lisbon to somewhere in the Caribbean or v-v) but I would not fancy rough weather on a small ship.