What is 0.75? Can you provide a complete statistics? Also try running the same benchmark with additional '-lavdopts lowres=1' option. Running mplayer as user should be ok, you don't need to run it as root. Additional option you may want to try is '-hardframedrop' (but you may get artefacts on screen).

Sharing this video somewhere would be the best option. At least we know how TCPMP handles it on a CPU with a comparable clock frequency.