We have the Big Arch in the states. Supposedly, it's 14 ounces. I started eating beef again this year, but I limit myself to the Quarter Pounder occasionally. Beef still has a lot of saturated fat but it also has a lot of protein.
I have had the big Arch a couple of times. It's more like a big Mac than a Whopper. The sauce is different than the big Mac sauce. It has a bit of a mustard taste to it. I believe it was only released in Canada and Portugal for the test market.