FALC0N :
If your using regular applications, then hyperthreading provides about a 20% speed boost. It's of no value for games.
More or less..
QUICK ANSWER:
Get the i5-3570K CPU.
SIDE NOTE:
*Haswell isn't out until roughly JUNE 2013 but some neat info has arrived:
- huge jump in power savings, especially in Idle
- overclocking features normally on motherboard being incorporated into CPU
- up to 3x iGPU boost (iGPU is finding a niche even for gamers who transcode)
- possibly improved addon graphics card shutdown to save power
- other Motherboard power saving features (confirmed)
- possibly further improved boot times
(a really, really cool feature is for laptops/tables though it MAY be there physically once desktop monitors add this feature. The CPU/GPU can shut down in milli/micro? seconds. So every spare moment nothing on the screen is updated the PC can sht down almost completely. This is achieved by the monitor having its own internal buffer for one screen image. The monitor just loops the small video buffer and tells the PC it can shut down. You can then SCROLL down the screen to read more, during which the PC starts the basic elements long enough for that task then shut down again.)
LONG ANSWER:
There has been very minor benefit to some games but generally it's quite limited. What is NOT CERTAIN is whether game engines can make use of this in the near future, such as the Unreal 4 engine.
There are two ways that the $100 or so can be spent for better performance elsewhere though:
1) RAM:
2133MHz vs 1600MHz has benefitted a few games now and will improve in the future (one game in particular improved by 15% at times).
*8GB DDR3 2133MHz is the max amount and frequency that will benefit a high-end machine.
2) GRAPHICS CARD:
Upgrading to a better graphics card will have a bigger boost usually than upgrading from 1600MHz to 2133MH of DDR3.
Hyper-Threading and real-world benefits:
a) Backing up C-Drive using a tool like Acronis True Image (free version from WD or Seagate if you have an Internal or USB drive from them).
*I hit 100% in all eight threads of my i7-3770K reducing time by perhaps 20%, though likely slower during phases that may not benefit.)
b) Video Edit or Conversion:
*Conversion CAN use all eight threads at times. Hardware decoding will mitigate the advantage here, and certain plugins aren't optimized.
**If you EDIT VIDEO (not just convert) then the AMOUNT of RAM is probably more important than having hyperthreading, or even the FREQUENCY
SUMMARY:
- Hyperthreading is generally a waste for most games
- Hyperthreading MAY benefit games in the future
- Upgrading RAM to 2133MHz, and/or graphics upgrade are better
- Hyperthreading can benefit transcoding, compression and similar tasks up to 20% at times
*Unless you intend to use a utility like Handbrake a fair amount I really can't recommend the cost difference for most people. There's better places to spend the money.