I did an upgrade about 2-3 years ago, so its not the latest hardware, and at the time, I didn't go for the top line/latest stuff. However, I lucked out and this PC even though being a few years old, runs like the clappers and its normally waiting on me!
Its basically an i7 3.5GHz 4 core (Hyperthreaded for 8 threads), with an Overclock to 4.4GHz. Something I found on the net, which only required changing 4 values in my BIOS, and it has run 100% reliably. Ironically, the MB came with an OC software, which caused common and random reboots all the time; so I do not run this at all. It was an upgrade, so I already happen to have a big boy cpu cooler (due to heating issues/bug with my previous bad/suspect dual core CPU). I also changed the primary HDD to a RAID 1 dual SSD (only 120GB because a few years back, when I built the system, these were just coming down in price). It only has 8GBG RAM, but I have 2 unused RAM slots for future upgrade (which I haven't felt I needed so far). The PC sits attached to my TV as my Media Center, and is also very quiet (I replaced all the fans with "silent" alternatives, and even have a spare random "silent" fan blowing across the MB, as my previous PC had a big power supply with extra outlets)
I do not use the PC for Gaming, so use the on-board graphics card on the motherboard. this fact shows in the windows performance index. Even running Windows (XP or Win7, Or Linux) in a Virtual PC appears to be "normal" ie I do not notice any "slow down".
If any of my friends were looking for a cheap but fast PC (not for gaming, a better video board may be all that is needed to be added) I would be suggesting this kind of setup. I have only seen it "bog down" when having to re-encode large video; but then I do this off my SSD and on my extra RAID 1 old school HDD. The big butt fan I have keeps the CPU sufficiently cool (ie no need for water cooling or crazy stuff)
NB, even though it is OC'd, please understand I am not one of those OC geeks that build their own water cooling etc etc, I simply applied the 4 values in BIOS I found on the net (specific to my CPU and MB I think) and off I went.bAlso remember when looking at the windows ratings of 7.8, that's on a scale from 1.0 to 7.9
I guess the moral of the story is, you do not need to spend up big. I lucked out, my PC combination just works, and works well.