The HD 6450 is likely borderline due to its 64-bit bus (unrelated to model name, per se). So, you can try both with and without PowerDVD option for hardware acceleration (also perhaps disable video processing options in both PDVD and CCC). Of course when HWA is disabled decode will rely upon the CPU. If that does not provide sufficient performance then it would probably be best to replace the GPU -maybe with at least a 6570 128-bit, 6670, or 7750.
"I beseech you, in the bowels of Christ, think it possible that you may be mistaken."