VDDC = Core voltage 😉
Technically it should do the same job! But afterburner comes with temperature gauges, GPU and CPU usage %, VRAM use... Fan profiling to modify your cooling potential...
Trixx should do just as well, but I've always preferred Afterburner for the extra functionality 😛
So i would use Afterburner, and Download some 3d benchmarks to compare results if you want to OC to the max Mhz (I did, but this takes lots of time! But then again you get 100% max performance)
so Furmark, MSI Kombustor... Any that you feel are right or look good 😀 They all do the same job (To ensure perfect stability I would try 3 different ones : Furmark or Kombustor, 3d mark firestorm and Unigine Heaven or Valley to get a good variety).
Once you are happy with playing around, get an idea of what does what.. You can think about pushing the card to it's maximum.
Read up on what the terms mean before overclocking it. Just to get a picture of what you are doing and why 😀
Enjoy the performance increase!