Mars999 IMO stick with your 2600k for a few years, no need to rush in and buy Haswell unless you have some specialized software you need to run on it or are a hardware junky that likes to play with the latest hardware, sit back and see how it goes
Benchpress, any windows OS before W7 SP1 does not support saving AVX registers after a context switch and therefore cannot run any AVX code successfully. AVX also does not play well with HTT if 2 threads running on 2 logical cores map to the same physical core so seems to me it's not as simple as it might sound. I really see little incentive for the majority of software houses to provide specialized code to run AVX2 code until there is an appreciable users market. How long have 64-bit processors been out and how long has it taken software houses to provide 64-bit software even though their compilers may have been able to produce 64-bit code from before 64-bit processors were released.
Why in a lot of cases have software houses produced 32-bit software where 64-bit might be more efficient, because 32-bit still gets the job done and works on more systems. If it turns out I have presumed wrongly regarding AVX2 that would be great but I don't have much hope for it being otherwise.
While these new instructions are powerful IMHO it will be a long time before they become mainstream so Mars999 just relax and see how things develop. For myself I have an oldish OC'd C2D laptop that will probably be due for replacing next year and in that case Haswell should make sense as I like to be able to get at least 5 years use out of it before upgrading.