5450 downclocks it's self

I have a DM4 with a 430m and a 5450 512mb GPU. I was just doing some testing running prime95 + furmark. After about an hour or so the CPU temps stabilized at 89/88C and 87C for the GPU. Then I noticed the temps went down about 5-8C across the board and checked the GPU clocks and it turned out the clock went down from 675mhz to 500mhz, but the memory was still at 800mhz.
Is it because the heat was too high? 87C doesn't seem too bad though. In GPU-Z it says the default clock is 500mhz, not 675mhz. Can someone explain to me what's going on here? Thanks.

 

GPUs are suppposed to be able to downclock themselves the save on power right? Kind of like the opposite of Turbo Boost on Intel's iX CPUs. Mine downclocks itself too.

 

But it was plugged in... so that shouldn't happen, not to mention it was being stressed to the max. Unless I'm missing something...

 

They shouldn't downclock themselves under load. It's likely that it hit some sort of thermal limit set in the BIOS and throttled itself to reduce heat. The Dell XPS 16 throttles the GPU at 84C, I've never hit that high, even with OC, but others in the XPS thread have. The GPU should be good to around 100C, and shouldn't throttle until over 90C, but sometimes the manufacturer will lower the temp threshold for an additional safety margin.