A couple of tons.....

I dunno actually, I'd say 1.5-2kgs, they're pretty heavy but super powerful. Our 3.2kg drum could spin up to full revs on a 2:1 ratio in less than 2s, so you wouldn't need 2.

As for the el'cheapo Speed900 from eBay I use one in BitzaWood. That spinds up 1.5kgs in a couple of seconds on a 2:1 ratio so pretty pleased with that.

Just remember that cheapo ones are only rated to 12v, whereas real Speed900s can do 24v. Our fan motor happily took 25.2v.