There is no reason to move from 4770k to 4790k...
Yes, there have been improvements to the thermal interface material & some extra capacitors to better handle the heat, but this doesn't magically mean every 4790k will hit higher frequencies than its predecessor. (it still depends on the batch for a good part).
The 4790k simply use more voltage to handle these already high stock frequencies, so this is literally just a factory overclock. (With ofc more heat and TDP).
They are just highly binned 4770k... at least we hope so
I don't know why some people had the hope of a big step up.
The best thing for 3770k & 4770k owners is still doing; delid, lap the IHS, and to use CLU as TIM (all at own risk) if done well and with passion, there will be a spectacular temp improvement.
There is no way; some improved TIM and extra capacitors will beat this combination I listed above. (Unless they return to use the solder as on the beast 2700k).
Another thing is if you have to build a whole new computer, then you can begin to think about it, and relative prices.
(and in most cases the Xeon E3 v3 family will be the winning choice @ power/price ratio "if intel does not understand this, in the long term, and raise/fix the prices of the whole thing").
@ orndorf;
You made the best choice.
If you go to open your chip (at your own risk) and you do everything perfect, as I said above you will have an improvement in temperatures almost scary, for sure you will be able to go up with frequencies quite a bit more, then for the stability etc. everything will depend once again from your batch.
Good luck.