So, I've always had trouble with the notion that stove-top temp is a good indicator of when to close the bypass damper for successful cat light-off. There are too many factors (slow time constant of most stove-tops, moisture baking off less-than-ideally-seasoned wood, starting flue and stove temps, etc.) to have any great correlation between cat or flue gas temps, and stove top temp. Thinking that flue temp must be a better metric than stove top temp, for this purpose, I've been shooting my single-wall stovepipe with the IR gun before engaging the cat. I find that I always get good light-off when the stove-pipe is close to 600F, and rarely if ever get light-off if the flue wall is under 500F. I'm not sure how well the stovepipe temp correlates to the flue gas temp, as that also has it's own time constants (heat sunk to stove and chimney liner at either end). Both stoves are down-draft catalytic, which is known to burn very well after light-off, but can be a little work to achieve light-off. I think it's time to install some flue probes.