I've tested viewfinder frame rate on 6600 and 6670. Result of 6600 is quite reasonable, 25fps at 160x120, 15fps at 320x240. But the result of 6670 test is dissapointing, only 7fps at both 160x120 and 320x240.
These result does not make sense since 6670 has better cpu and newer software. Does 6670 have a slower camera module or lower bandwidth between cpu and camera?