Do synthetic benchmark temps matter

[Eyesthetics]

My i5 4690k is running at 4,6Fhz 1.295V. When stress testing using OCCT the temps hit 87c albeit for a few seconds then it went down to 78c then 82c.I'm using a corsair h100i

But when playing cpu intensive games like watch dogs the temps max out at 72c.

Is it safe to keep this oc?

[Faceman]

Yes, those gaming temps are fine.  You want to keep it below 85C.

[Enderman]

those temps are fine

[Eyesthetics]

Why are benchmark temps so high even with h100i?

[Django]

Temperatures will depend on local ambient temperature, power consumed and cooling solution.

[blackadder]

Why are benchmark temps so high even with h100i?

the benchmarks really stress the crap out of your system.  your oc is safe if its stable. test it for a few hours.

you temps don't seem wrong or unsafe but, you could always remount the cooler and see if temps decrease.

[LogicalDrm]

Stress test temps are nice way to see if everything is working and would PC stay at safe level if it runs into unexpected loads. You could get close to artificial load temps with rendering for hours.

[Queek]

Yes that OC is safe to keep.  Those temps are an extreme case, and will probably only show up during sustained high loads (as LoGiCalDrm said).  

I would recommend switching to adaptive mode, which will keep your temps low much of the time.  On adaptive, my 4690k sits at 35°C almost all the time, but can boost up to 4.6 GHz when I need it.