sony 70-400 vs tamron 200-500

I retested today (cloudy) with a different camera- the sony A700 and there is almost no difference between the lenses.  Or rather the difference is not favoring the tamron. Sometimes one lens is slightly sharper and sometimes the other lens is.

my original tests were on the sony 580.  COuld this have to do with the diff. in mexapixels in each camera?????  Or what????  even though the diff might not be apparent in my samples it is at my end with the 580 but not with the 700 camera.

Agree that handholding can make a difference.  and I do shake a bit more with the sony 70-400.

will try them on a tripod eventually.   no point in trying them in raw as someone suggested as I never shoot raw.

thanks for any thoughts.