After checking out the C4S profile I would say your car is well on its way to becoming a dedicated track car and that's a great thing
1) What brand/type/viscocity oil do you currently use?
2) How often do you change the oil?
3) 250 degrees is TOO HOT!
4) How much $$ is a new 993 motor?
My guess is that the cost ($1700) isn't too much in the greater scheme, given your current mods. Heck, a new set of "r" compounds would cost close to that for your car.
Make sure to check your current system. By that, make sure the thermostats are working properly. I don't know exactly the location of the factory oil cooler, but is there any way to increase airflow over it?