Best gaming systems I know are a balance.
For example they pick from the list I noted within their budget and have read the following a lot of times.
"Our tests demonstrate fairly little difference between a $225 LGA 1155 Core i5-2500K and a $1000 LGA 2011 Core i7-3960X, even when three-way graphics card configurations are involved. It turns out that memory bandwidth and PCIe throughput don't hold back the performance of existing Sandy Bridge-based machines. "
So that covers the GPU and CPU. For the HDD my nod is to that hybrid 750GB 7200 2.5 inch drive. Best of both worlds without the pain.