the one I demo with is 1 1/2"x3" on the top and I've forged 2lb axes and 10" drawknives on it at shows using the Iron age forge!
But; you're Dave Budd.
I've also heard the silicon tip works wonders. The main problem with my head anvil is I could never get the face flat. Right annoys me. Still, it won't be going in the bin, like!