Expectations for over-occupancy permit for venue?

My venue is a museum and not typically used for wedding receptions. We'll be clearing out the exhibits, so there will be room for more people than the stated occupancy in the placard on the wall. I'm looking into getting an over-occupancy permit through our local fire marshal. However, the placard says 101, and we want to invite 200 (more if we could - big families ugh). The fire marshal will have to come out and measure, calculate based on code, and then tell me the number. But we want to get our STDs out the door ASAP, and now I've scared myself about committing to this venue. We did recreate the floor-plans and know that we can fit 200 with tables!! As well as cake table, bar, dance floor, etc. (But I don't know if the fire marshal will agree.) Does anyone have a sense of how much an over-occupancy permit usually allows? I know it depends on specific local codes, but is 100% increase feasible? Has anyone done this?