Originally Posted by DeanM
Big difference. I7 idles in the mid 40s. I3 idles in the low 30s. And those temps are with an absolute giant HSF on the i7... stock HSF on the i3.
You have to have the same system, with the same software and same peripherals, in the same case and location, doing the same thing, to compare two systems.
SilentPCReview has reported in its tests of the various Sandy Bridge processors that the power consumption at idle and in playing an H264 video (which they characterize as "light load") for these processors are as follows. (I've also included Passmark scores to give some indication of the relative power of these processors). Note that these levels are while using a discrete video card, NOT the integrated graphics, which they do because in these articles they also compare AMD chips like Phenoms and Athlons that don't have integrated graphics. But they still give a true representation of the relative power consumption of these chips.
Processor Idle W / H264 playback W / Passmark Score
Typically we're putting i7s in heavier duty builds with bigger motherboards, more drives, bigger PSU, and more peripherals, so they may look like they use more power. And certainly under full load they draw more power, but it's questionable whether then end up using more power to complete a specific task because, except in things like watching a video where the time required is fixed, they get the task done more quickly.
But the point is that at idle and under light loads like watching video (and in contrast to previous generations of processors where quad cores were generally power hogging heat monsters) these new chips use almost the identical amount of power even though they represent a vast range of processing power.
So, for an HTPC, it's doubtful that you pay any significant penalty in terms of heat/cooling/noise to use an i5 rather than an i3 because for most of what you would be doing they're going to use about the same power. And for those few processing power intensive HTPC tasks like encoding, you'll obviously get the job done quicker (although then you will be using more wattage and generating more heat). But the primary drawback is simply that it's a waste of money because that video isn't going to look any better on the more powerful machine. But if you want to waste the money, I don't see any other major drawback, unlike in the past when using too much cpu was counterproductive in terms of keeping the maching quiet.
Indeed, I'll confess that I'm seriously considering putting an i5-3450 in an upcoming ITX htpc build, just for the hell of it, and because at $149 (Micro Center) it's a great buy for a monster of a cpu. Yes, I know it's unecessary and overkill, but hey, it's fun.