To get an idea how hot your engine is getting, I would suggest getting a temperature indicating dipstick .
Or depending on how involved you want to get with this, you could install an electrical temperature indicator and a sensor that replaces the oil sump drainplug .
If by chance you go with an oil cooler the OEM kit from BMW, the most costly part , the thermostatic bypass valve that goes in place of oil filter cover, won't fit, it won't clear the right header pipe .
Using a semi-synthetic or full synthetic oil could be help if you find your engine is running hot .