Ok, a couple of things.
That dell optiplex 780 is not a good idea. We had a few of them at UEI college, and other than barely supporting the hardware virtualization support needed for a modern virtualbox experience, you can still tell the age. Plus their built-in graphics support seems about on par with what onboard quality was in 2003.
Second, overclocking is a bit hit and miss, heavily depending on what CPU, mobo, RAM, GPU, and cooling you have.
For example, some chips, like mine, an AMD E-1200 APU, are clocked completely below what they can actually handle. Stock clock is 1.4ghz, but you can boost that to 2.3ghz on stock cooling alone, with tempertures under load being about 65c. That's roughly a 90% overclock.
Then there's my wife's system, running an AMD A8-3500m APU quad core with stock clock at 1.5ghz, and 8GB of RAM. Very similar to one of the system's you were considering. Turns out, after I did a little investigating, the A-series APU's have a "turbo boost" mode where they auto-overclock, if need be. In my wife's case it goes from 1.5 > 2.4Ghz without telling you, under load. Needless to say, that little fact made my wife happy that her system can indeed handle sims 4. I'm just glad I don't have to buy her a new laptop for one game.
These are both cases where the manufacturer purposesly does not run the chip at its theorectical full power in order to make it a cheaper, (crappier?) component. In turn, it makes it look like the chip is a candidate for massive overclocking stunts.
Other chips come stock right out of the factory clocked as fast as the manufacturer knows it can go. Those are the ones where overclocking capacity is very little on stock cooling. I think the 3.0ghz P4 chips are in this category, as I remember the reason intel stopped the clockspeed wars with this chip due to it just failing after 3ghz, considering it a literal dead end and going on to create the more modern coreduo/core2duo/core iX architecture.
That being said, I haven't done much research on overclocking P4's, as their age may mean the overclocking may not matter if they simplely can't do enough instructions per clock to handle modern multithreaded software.
) over VPN. Since RD is encrypted and so is the VPN, the data stream is encrypted twice.