Is five pounds a week a feasible loss, given that I'm 6'3", probably about 245?

I think it is feasible to lose 5 lbs a week in the first few weeks but I doubt it will continue at this rate.

It all depends on how your body works too, maintaining at 5000 cals a day may not work for everyone. Give it a shot with the right amount of calories (don't go too low) and exercise and see what happens.

I think if someone is in a higher weight range i.e. very overweight or obese it's reasonable and safe to loose more than the suggested 1-2 lbs a week.

I think it's possible.
I went on the south beach diet, and the first week I lost five pounds. I'm only 5'2, and when starting the diet weighted 135. Since then, I've lost 1 pound steadily ever since.. So, don't expect that you will lose 5 lbs/week all the time. It will most likelly slow down to 1-2lbs/week.