I have shot an mule deer with a 338-378imp with a 300gr. smk and it blew and softball size entrance hole and no exit at about 40yrds. I have used a 142gr. smk out of a 6.5x284 and it was about 200yrds on an mule deer and it performed very well. Good penetration and expansion. I also used that combo on another muledeer at about 360yrds and it kinda just penciled through with little expansion but there was some.
I dont know who ever came up with the imaganary word of "Over Gunned"