Cooling the oil won't cool the heads...
Head and oil temps are totally separate entitiesand are impacted by many different things from RPM (oil temp) to load (head temp)...
Your stock cooling system is more than likely adequate and will probably perform better than the 911 systems. I have tested 911 systems comprehensively compared them all off the shelf and lemme tell ya that no one has done any development with them. I did this testing to see and prove just how good my DTM cooling system was and I was amazed.
At your altitude the higher CR may make the engine run cooler through better efficiency. When I build engines to operate constantly at altitude I run more CR with the combo to make up for the less dense air. Doing so typically ups efficiency and incread efficiency makes for cooler running.
For you the key component is the camshaft undoubtedly- The stock cam is horrible, especially at altitude. "Its all in the combo" meaning you have total control of the outcome, make wise decisions and do your homework.
If it does run too hot, here is your answer. Its scheduled for a Christmas release date and has been in testing here for over a solid year.
914 DTM