Intel Core i5-3570K advantages
-This microprocessor has unlocked clock multiplier. The CPU can be freely overclocked on most motherboards if greater performance is required.
-The Intel i5-3570K is 8% more energy efficient.
Intel Core i5-4670K advantages
-Single-threaded performance of the CPU is higher.
-The Intel Core i5-4670K is 6% faster in multi-threaded programs.
-Memory performance of the processor is better.
-The i5-4670K includes AVX2 instructions, introduced in the recent past. These extensions are not broadly used by applications yet, but their support should improve in future apps.
-FMA3 instructions are enabled on this CPU. This technology is only available on AMD microprocessors, for that reason it may not get broad support from software vendors.
-The 4670K is less energy efficient under load, because Intel integrated VRM on the chip. It has lower idle power, but the comparison is for the maximum power consumption. Total system power consumption could be the same, though, but I can't confirm it.
Link:
http://www.cpu-world.com/Compare/579/Intel_Core_i5_i5-3570K_vs_Intel_Core_i5_i5-4670K.html
In my opinion:
- (With Overclocking) If you plan to upgrade sooner than 2 years go 1150, if not go 1155 as in 2 years 1150 will propably/might change. Keep in mind the increased price of a 1150 motherboard as it is new. New is nice but it is untested also. There is not a big difference between them in performance. Personaly I'd go with 3570K as it is "safer", easier and more "boostable" to overclocked and I'd go to an upgrade after 2 years as 3570K I believe it'd keep me up in gaming for that time.
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(Without overclocking) Don't go for a "K" as mentioned from poster above. Play safe and go with 1150 so you got the option of upgrading in near future if not pleased with 4670K (and have a procceessor with good aftersale price for the near future).