It should be enough.
I found 2 1080p trailers in mp4 format : cpu usage often reach 100%
while playing ( via FLV player or PwrDVD9 ) these, both picture &
sound have pauses.

With Nvidia VDPAU,
it probably wouldn't need more than 10% of the cpu.
I'll buy & fit 1 of these decoders, & hope to decode @ even 8x speed.