To answer your question, yes, the sensation comes with thermal protection that helps against overheating. If the device becomes to hot, it(in most cases) shuts itself down until it cools. The CPU in the sensation is underclocked when it's shipped at 1.2Ghz(1188), but the true spec of the CPU is actually 1.5Ghz(1536). HTC underclocks the CPU to 1.2 to save on battery consumption. I personally have ran my phone just fine at the 1.5Ghz setting, I've even pushed it up to 1.6Ghz(1620) and it ran fine with the exception it did get just a little hot, but nothing to worry me. That being said I've since underclocked my CPU to 1296 and all is well. And afterall, how fast do you really need your phone to be before you take it too far and fry the cpu?? The sensation is fast right out of the box and even faster when using a NO sense rom, such as cm7(my personal fav)
Side Note : The new sensation XE ships with the cpu at it's original clock speed of 1.5Ghz.. both sensations have the 'exact' same cpu.
In regards to your GPU question, I have mine set @ 300mhz and not 320. The sensations GPU comes clocked at 266.I've ran it @ 320 and it ran just fine.. for me it's more of a personal preference. My graphics look just fine clocked @ 300mhz.. Below is a quote about the chipset and the new one coming out.
"With Adreno 225 Qualcomm improves performance along two vectors, the first being clock speed. While Adreno 220 (used in the MSM8660) ran at 266MHz, Adreno 225 runs at 400MHz thanks to 28nm. Secondly, Qualcomm tells us Adreno 225 is accompanied by "significant driver improvements". Keeping in mind the sheer amount of compute potential of the Adreno 22x family, it only makes sense that driver improvements could unlock a lot of performance. Qualcomm expects the 225 to be 50% faster than the outgoing 220."
if this helped, give the thank you button a punch
p.s. I've ran both insertcoin & revolution HD and both ran fine.. I just really prefer no sense roms