A bad amount is 95 minutes of cardio!
Unless you are training for a marathon, there's no good reason to do more than 45 mins of cardio. 95 mins pushes you catabolic and you start tearing down muscle fibers.
Mix up your cardio...ride a bike, use the stairmaster, hop on the eliptical. GET YOUR HEART RATE UP! Its not cardio unless you get the heart rate up enough to actually get a cardiovascular workout.
Slow, plodding cardio isn't nearly as effective as 'real' cardio.
As for the heart of your question though, yes 600cals at a slow inclined walk for 95mins sounds right...in fact it sounds a little high. When I do the eliptical for 40 mins and maintain a heartrate above 140bpm (not exceeding 165bpm) I burn about 300 cals, and that's with varying resistence and incline.
You can't fix your body with exercise alone...yes it makes a huge difference, but diet is key. If you aren't creating a 500calorie deficit through diet, the cardio isn't going to shed much fat. It may give you a strong heart, but it won't shed a lot of fat.