MHO:
A custom bike is more ideal. I'd take that $400+ and upgrade your bike unless your ready for a new frame, then go for it as long as you really dig the frame that comes with that complete you choose. Because as soon as you start riding that bike you'll be noticing things you want to mod, and mod it you will. If you start with what you have and pick your prefered parts, once your ready for a new frame you have your dream bike of the moment.
Of course we're never satisfied were human.