What actually determined a frigate's speed

Could a ship of the line outsail a frigate in heavy weather?

Sometimes, but weather, hull condition, sail area, ship size, and the skill of the captain, sailing master, and crew all affected the result.

A larger ship could gain advantages from mass, length, and the sail it could carry in heavy weather, but heavy frigates and razees also mounted large sail plans for their size. Fouling accumulated during a commission, and inadequate overseas docking infrastructure could erode a ship's expected speed. Seamanship and maintenance were therefore part of combat capability rather than background details.