The question is not "How fast do you want your PC to go?" No, the real question you have to ask yourself when it comes to upgrading a gaming PC is "How fast do you want to spend your money?"
The reason for this is that performance costs money, but the performance/cost curve isn't a linear one, it's exponential, which means that the jump from mid-range performance to high-end performance - also known as "enthusiast" level performance - is going to mean a far bigger spend than going from budget to mid-range. It's just a fact of life that hardware makers put a huge markup on the top-end gear.
With that firmly in mind, let's look at how you can supercharge your gaming PC by spending a lot of money very quickly.
At the heart of any gaming PC is a decent graphics card. This is the part that does the majority of the hard work, so if you want to supercharge a gaming PC, this is the place to look first.
If you want high-end, there's two cards to look at. The first is the monster Nvidia GeForce Titan Z. This features twin GK110 chips, 12GB of GDDR5 RAM, and has 5,760 CUDA cores.
If you want this inside you PC, expect to get no more than a few pennies of change from $2,000.
A cheaper way to get a top-end card is to go for an AMD offering, which currently is the Radeon R9 295x2. Sandwiched into this card is two Radeon R9 295 processors and 8GB of GDDR5 RAM. Not as impressive as the Nvidia offering, but for around $650 it comes in at a more reasonable price.
And if one of these cards isn't enough, then pop two or three into a motherboard that supports that sort of power - if you still have money that is.
Hard drives are out, replaced by the much faster solid-state drives. When it comes to performance I recommend going for the SanDisk Extreme PRO line, which spans from 240GB which you can pick up for around $150 to 1TB which will set you back around $450.
You need something really good when you're pushing a PC to the redline. There are lots of brands out there to choose from, and I've had great success with the G.SKILL Trident series. This will set you back some $140 for 16GB.
Might seem odd to have the processor listed last, but it's only if all the other components are up to scratch will you get the full benefit of a high-end processor. But if everything else is sorted, you can start spending some serious money on silicon.
On the Intel front you have the octa-core 3.0GHz Intel Core i7-5960X Haswell-E, which will set you back a whisker over $1,000. If you want a motherboard to pair this with, I suggest the $400 Asus X99-Deluxe/U3.1, which will give you a huge amount of leeway for performance tuning and overclocking.
If you are more on an AMD fan - and want something cheaper than the Intel silicon - then the chip to look for is octa-core 4.7GHz FX-9590 Vishera Black Edition, which has a more palatable $240 price tag. Pair this with a $170 Asus Sabertooth 990FX motherboard and you have a superb gaming platform.