I have a hard time with finding just the right hammer. I don't use any flat stock. I don't even own any!
Most of my forging is with 5160, but I have 2400 feet of 1 inch square stock made back in '84. So, I use my power hammer to knock it fairly flat to about .275 - .300 and about 1 1/4 wide. Then I forge my knives from that. When I say I "forge" a knife, I really "forge" a knife! My W1 knives come down from 1 or 1 1/8" round. So, anyway, I have a lot of steel to move around. It takes me about an hour to forge a simple 5 inch hunter. But I know I can cut that time down a little if I had just the right hammer to move the steel a little more efficiently.
I'm always in search of the right hammer!