So, you're doing some kind of high energy discharge thing, and using your circuit to get precision measurements of the time when the cap voltage passes certain points? Or are you using it during the charge stage, so you know when to stop charging?
If it's the former, then you will probably want to use higher speed comparators, like the LM311.
Otherwise, the 741 would be fine.
You probably will want more resistance in the divider, though, as there's no reason for it to be dissipating anything on the order of 50W. You could use a divider that's more like 50M in series with 50k, as the output impedance will still be a bit under 50k. Then, you're using less than a watt.
I'd also go with what the other guys said, and string a bunch of resistors together in series to make the 50M--maybe 33 1.5M resistors and a 500k (they can all be 1/4 watt though) to keep them each at 200V.