For 12 hour trips I've been on, New Buc cruises about 25kts for a roughly 4 hours, so whatever that distance works out to be with the occassional weaving/tacking so we don't get beat up on waves.
Expect shoulder to shoulder with 100 people during red snapper season.
BOOKING — Galveston Party Boats INC
Still cheaper and worth the occasional line crossing than buying, storing, towing and maintaining my own boat capable of going that far.