for a motherboard, you can't say whether its powerful or not, because it simply brings all the different parts of the computer together, the "powerful" part comes from components like the CPU, video card, etc.. different motherboards come in different sockets and have many different features and thats why there are so many out there with varying prices..
as for video cards, you have things like core clock speed, memory size, memory speed, number of pipelines, pixel shaders, memory bandwidth, and a whooole lot of other things that make up a video card... but even the biggest expert won't really know how good a video card is until its tested and benchmarked. thats how we know what video cards are good and which aren't so good, we look up benchmarks made by various websites testing different cards against eachother.
"Is virtue a thing remote? I wish to be virtuous, and lo! Virtue is at hand." -Confucius