A suggestion to improve build applications

[Apuly]

the Newegg page for the HIS 6850 lists a 500w PSU as a "requirement." Should I be concerned about the 450w PSU in the case?

Yes. However, you should be able to increase the wattage of PSU by first putting a conductive object, like a knife, into the the energy socket which provides energy. Doing this will increase the amount of electricity that flows trough the socket, and thus increase the wattage of your PSU by about 60-70 watt.