The new SS cats are "Hyperactive" for a while after you first use them, then settle down and need higher light off temps. I could engage at 200F with mine at first, and later I was engaging above 250F to get lightoff.
Yes, there's that, and there is also the fact that the stainless cat was "improved" for this fall. There were, um, issues with the first batch *cough*defective*cough*. I and several well-known Woodstock burners with years of experience and dry wood had problems last season with the new steel cats and sent them in for testing. I called Woodstock in August to see where they were on this. They told me that the structure of the cat did not allow for even flow and that a new batch was being made with a more, um, uniform(?) construction technique like used in the cat for the Progress to promote better flow.
I got an e-mail a few weeks later saying that the new cats were in, if I would like to order one. I get the new cat, and it looks exactly like the old cat, like it's made by rolling up a sheet of the stuff and then squishing it into a rectangle. So, I call, and I'm told that the new cats are constructed the same way, just with a different wash coat and different/better braising, and the appearance is identical. I have not yet fired up he stove this season, so I can't comment on the performance of the new cat.
If you got your stove before September, and it has a steel cat, it is probably NOT the "improved" cat.
[Edit: Only Fireview cats have been revised, not Keystone cats.]
It would be nice if someone from Woodstock would post a definitive position on this cat issue.
I also asked about gasket issues with the steel cats, because my gasket was disintegrating, even though I had not removed the cat from the frame since installing it. I was told that the interam gasket would probably need replacement every year and to wrap it around the cat 1.5 times.