Here to confirm that blocking off old empty quarrys that you have no use for is great for FPS.
Though rather than drawbridges. Since I'll often use the first level quarry as a farmign space, and the lower floors were accessed by stair. I jsut put a hatch on the stair and forbid it. Seems to end up with teh same boost to FPS as drawbridging everything. And is better in the long run than channeling because I have more useful space with floors and ceilings to be used in the future.
Example.
I've recently been doing a "Single Pick Challenge" type fort. (ver 34, gonna wait 1 more patch before digging into 40)
After getting to the caverns, walling myself in for defense. Started mining out a large area for stone to make crafts to trade. Cleared a 50x50 area of 4z levels over the course of a year with my dorfs (got more than 1 pick after first caravan) Blocked them off for a while because they were useless. Started to run short on food and wood due to the lack of suitable growing area after my fort spiked from 22-48. So using those cleared floors, and a bit of work. I diverted an aquifer to them for a short bit to mud 3 of the levels, and leaving level 4 with all the excess water as storage for the future. 3 new 50x50 growing areas, rather than 1 I would have had with channeling. (Only ended up using about half the first layer for a number of years, but the other 2 started growing trees which are always in short supply in cavern fortresses)