I will build myself a slim itx system for internet, multimedia, programming, software engineering, web developing, blogging and, maybe, some very casual and very light gaming (source engine)... I want it to be CPU powerful, as graphics are secondary here.
My budget top options are the i5 4430 and the A10 6800K. Both have decent IGP but I do not know the difference between them. In case I would go with the AMD, would be there a significantly CPU power sacrifice in order to get a bit gpu boost?
In general Intel Haswell CPUs are more powerful than what AMD has to offer. AMD's APU have the lowest processing capabilities of the three so if CPU performance is important take them off your list.
You are now left with the AMD FX Piledriver generation and Intel Haswell generation CPUs. However, the FX series CPUs do not have in iGPU, the means you are left with Intel's Haswell CPUs.
From an iGPU point of view the most powerful one is the Radeon HD 8670D found in the A10-6700 and A10-6800k. It's performance is basically equal to a Radeon HD 6670 DDR3 graphics card when DDR3-2133 is used. It's performance is about halfway between the Radeon HD 5570 and Radeon HD 5670. In more modern terms it is slower than the Radeon HD 6570. The most powerful Intel iGPU is the Intel HD 4600, it's performance is basically equal to the Radeon HD 5570.
For everyday usage either the i5-4430 or the A10-6800k will suffice. For anything that is processor intensive like compiling and lots of number crunching you want the i5-4430. From a gaming perspective, you will want the A10-6800k.