A Single core performance has improved by an average of 30% per year for the last five years.
Back the late nineties the rate of increase in cpu horsepower was phenomenal, every two years processor throughput was doubling. As clock speeds reached 3 and then 4 GHz the emphasis shifted from linear single processor speed to multi-threaded performance. There has been a relatively slow and predictable improvement in performance over the last five years and there is no longer the need to upgrade a CPU more than once every three years. In terms of single core performance, a reasonable proxy for real world performance, the late 2007 Core2 Duo E6550 scored 881 points on PassMark-S vs 2080 points achieved by the Mid 2012 Core i7 3770K, roughly a 140% increase in performance over the last five years or roughly a thirty percent improvement per year.

The Best.
CPUGPUSSD
Intel Core i7-8700K $370Nvidia GTX 1070 $357Samsung 850 Evo 250GB $90
AMD Ryzen 5 1600 $144Nvidia GTX 1060-6GB $220Samsung 850 Evo 500GB $110
Intel Core i5-8600K $260Nvidia GTX 1080-Ti $808Samsung 850 Pro 256GB $97
HDDRAMUSB
Seagate Barracuda 1TB (2016) $43Corsair Vengeance LPX DDR4 3000 C15 2x8GB $105SanDisk Extreme 64GB $43
Seagate Barracuda 3TB (2016) $85G.SKILL Trident Z DDR4 3200 C14 4x16GB $939SanDisk Extreme 32GB $48
WD Blue 1TB (2012) $45Corsair Vengeance LPX DDR4 3200 C16 2x8GB $120SanDisk Ultra Fit 32GB $12
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