original r280 (without MMX quant_4x4/8x8)

./x264 --direct temporal --analyse all --me umh --subme 6 --8x8dct --filter -2,-2 --bitrate 1000 -v test.yuv -o test.mp4 720x480

  %   cumulative   self              self     total
 time   seconds   seconds    calls   s/call   s/call  name
 11.09    127.80   127.80 60132914     0.00     0.00  quant_4x4
  5.32    189.12    61.32                             x264_pixel_satd_8x8_mmxext
  4.65    242.73    53.61  2782140     0.00     0.00  x264_macroblock_encode
  4.59    295.65    52.92 175082977     0.00     0.00  x264_cabac_encode_decision
  3.96    341.30    45.65                             x264_mc_chroma_sse
  3.96    386.90    45.60  3869124     0.00     0.00  x264_me_search_ref
  3.63    428.72    41.82                             x264_pixel_sad_8x8_mmxext
  3.43    468.20    39.48  5194868     0.00     0.00  quant_8x8
  3.27    505.90    37.70 51862176     0.00     0.00  x264_mb_dequant_4x4
  3.17    542.42    36.52 15667975     0.00     0.00  block_residual_write_cabac 

total time         1152.01

--------

(with MMX quant_4x4/8x8)

  %   cumulative   self              self     total
 time   seconds   seconds    calls   s/call   s/call  name
  6.17     63.23    63.23                             x264_pixel_satd_8x8_mmxext
  5.01    114.60    51.37  2782140     0.00     0.00  x264_macroblock_encode
  4.82    164.01    49.41 175082977     0.00     0.00  x264_cabac_encode_decision
  4.39    209.03    45.02  3869124     0.00     0.00  x264_me_search_ref
  4.36    253.72    44.69                             x264_mc_chroma_sse
  3.99    294.58    40.86                             x264_pixel_sad_8x8_mmxext
  3.63    331.78    37.20 51862176     0.00     0.00  x264_mb_dequant_4x4
  3.61    368.73    36.95 15667975     0.00     0.00  block_residual_write_cabac
  3.56    405.17    36.44  4330144     0.00     0.00  add8x8_idct8
  3.41    440.13    34.96                             x264_pixel_satd_4x4_mmxext 
...
  2.71    563.15    27.74                             quant_4x4_core_mmxext
  1.01    719.70    10.40 60132914     0.00     0.00  quant_4x4
  0.87    768.55     8.93                             quant_8x8_core_mmxext
  0.10   1006.30     1.04  5194868     0.00     0.00  quant_8x8

total time         1024.90