Do I need scores to prove the power of this system?
Not for us you don't. (if you post it on craigslist or ebay that may help sell it thou) We all more then understand what it's capable of.
The reason your getting lower budget prices is a used computer just isn't worth much. As soon as you build it and use it. It drops in value (usually by about half). Just like when you drive a new car off the lot. You may have paid 35k for that car but once those tires roll onto the street don't expect more then 18k from a dealership for trade in value.