You need to check the engine manufacturer to see the maximum temp allowed for their cylinder. Most aircraft engines list something over 500 and usually 550 as maximum. However, for long life it is best to keep it below 400 if you can. I size my oil cooler to keep the temps down to 400 at cruise and I never let it get over 450. I'll slow down or shut down if I see the temps get close to 450. I usually get max oil temp at 170 also but I have seen as much as 190.
A large oil cooler doesn't do it all. I had a huge oil cooler on one engine that never got over 140 and I could still get high cylinder head temps if I pushed it too hard. Do what it takes to keep the temps below 450 and you'll run for a long time.