Quite honestly, the 4770k easily outperforms the 3820 in everything. The 3820 does not have a completely unlocked multiplier, it has a limit. The 4770k is faster clock for clock, but also overclocks higher and easier (you can just use the multiplier to overclock, no need to touch the base clock).
Also, motherboards for the 4770k are 1/2 as much. Case in point, this ASRock board has tons of bells and whistles for only $170!
http://www.newegg.com/Product/Product.aspx?Item=N82E16813157371
Being able to future upgrade to a hex core is not worth the current price you'd pay for outdated hardware now. Plus, the 4770k competes against the 3930k hex core quite well, and is only slightly slower in heavily threaded applications.
Take a look at the bench comparisons-
http://www.anandtech.com/bench/Product/836?vs=552
90% of applications are only single threaded, which the 4770k is the king of. 7% more use 4 or less threads, and only 3% of things you can do on a PC can utilize more than 4 threads (though the 4770k has 8 threads so it's still not slow at anything).
So, the motherboard/cpu combo you'd be saving $90 on, the 4770k is far more energy efficient, it's the latest cutting edge technology not a year and a half old, the CPU coolers for it are more readily available and are cheaper, it overclocks easier, runs cooler, and is faster in most applications than even a 3930k.