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>The numbers you want to look at are CPU and HD temperatures. You don't really want those going far above 70 and 55 respectively. (On my desktop, full-on Prime95 gets the CPU no higher than 59C.)
70C is about right for CPUs, that's Intel's recommended max temp for their modern CPUs, anyway - the chips won't start falling over until >100C, but they'll still function fine at 80-90, you're just running the risk of shortening their lifespan. It's worth pointing out that some models of GPU have, by design, been running at 95C as their intended standard temperature for years now:
With respect, I'm not sure why you'd prioritise monitoring HDD temp as they never get particularly hot; unlike CPU/GPU, they don't get much hotter from working harder. Monitoring CPU/GPU temps is significantly more important as they fluctuate to a much greater degree, and both are dependent on heatsinks and fans to keep them cool. Heatsinks get clogged with dust, fans can break. HDDs just sit there.
The renderer on the PC port of GTA IV is fucking useless and not a good indicator of anything much, incidentally. But yeah, get speccy or hwmonitor and check what temperatures you're seeing with various games and go from there.