I'm not sure what the flue temps are but since taking that picture I have moved the thermometer to the cast iron, just to the left and right of the flue opening. I have two thermometers, only because I didn't fully trust my first one after my son was found to be playing with it when the stove was cold.
I have found that reading (from having a thermometer in both places) to be just slightly higher (20-30 degrees) than the reading I would get on the stove top WITHOUT the cook top installed. When speaking to the kind folks at Woodstock, we talked about placement of the thermometer and really the only reason they like the spot next to the flue opening is because your thermometer will be more sensitive to the changing temperatures so that you can more quickly engage the catalyst.
If you're a person like me who rarely drops out of the catalyst range when burning (24/7 and very warm to heat 1800 sf of poorly insulated space) the stove top is just as good. However, personally I don't trust the reading on the stove top with the cook top on. I had a cook top without the heat shield that cracked, I think the stove was actually operating at a lower temperature overall but that the cook top was getting super heated and giving me a bloated stove top reading. I just installed a new cook top yesterday that has the heat shield but I haven't bothered to take the stove top temperature since I like where the thermometers are.
A 600 degree reading is well within the higher end of the operating limits of the stove.
There are a lot of people who never get close to that, but we all live in different homes with different levels of insulation, different square footage, different ceiling heights, in different climates etc, etc, etc...
These forums can drive you nuts if you're trying to come here to determine a good operating range for your stove, based on all of the information other people have posted for the same stove. The real question is "is this stove heating my space the way I want it to?" if the answer is yes, then great!