You can find the test of both television
40V4000
LE40A656
Both are very good television, the Sammy have a good point with 100Hz motion treatment, but have problems of lags with ps3/xbox and some problems with the 24hz on blurays (which can be resolve with a firmware update).
The 40V4000 is a very good television even without 100 hz and 10bit panel. Very similar to the 40W4000 which is one of the best tv of the year.
The test are very precise so you can make your choice.
And if you ask me, i would recommend the 40V4000, the best is to ask questions about pros and cons of the tv on both topic (each one has a specific thread on this forum)