This Intermec Vocollect movie gives an example of some differences between voice picking and picking via RF.
OK, it may be a little exaggerated, but have a look and judge for your self. We are convinced Voice Picking will almost always work faster. The how much will depend on many aspects (walking difference does not change so the more your workers walk, the smaller the % of gain - and a lot will also depend on how ergonomic your RF works (barcodes easy to scan, materials easily picked with 1 hand....).