Calm Kelpie is far FAR outclassed by Timid imo... but it does force a lot of switches regerdless. Once you get a SubCM up tho, speed will be the only thing stopping you.
With Calm Nature, you fail to outspeed positive natured and fully invested base 100 speed pokemon (Staraptor, Mega Charizard X and Y, Mega Gardevoir etc). imo, it would be preferable to ditch this one and find a Timid one unless you're desperate.