In years past you could determine the speed of a processor based on ghz, but now there is much more that goes into it. What is the exact processor you are looking into?
Also, if you had trouble with your last build, then just do some reading and try to get it right the second time. The parts you buy to build yourself are as good or better then the parts dell with slop together for you. Plus, a hard drive malfunction is not a big deal, a replacement would cost $50-100.
Also, about sound... the quality of integrated sound depends on the board, but generally I have found integrated to be sufficient.