Yes and no. Clearance section can go as high as 50-60% off but sizes are very limited. I will say tho that Red Fleece stuff are always discounted heavily on clearance since they're not hugely popular line for BB. I think partly due to everything RF are extra-slim fit / milano fit with the jackets/shirts and pants.
Black fleece are better quality than regular BB but they're pretty overpriced IMO. 40% off BF is not rare occurrence. I bought a BF linen shirt for 60% off clearance as well.
In my view, when to buy Black Fleece depends what you're looking for. If you want a staple like a solid OCBD, or you want to buy a seasonal item that may sell out, then the corporate sale (30% off) is as good as time as any. But, if you're looking for something else, and willing to take the chance that it will still be around, then you're better off waiting for the clearance sales, which range from 50% to as much as 80% off.
If you want to buy some of the more outlandish (in my opinion) stuff, more than likely, it will still be around when the big-time discounts roll in. And if you don't see it online, then your sales associate can try to track it down from one of the major Brooks stores, or from the BF boutiques in NY or SF.