338 Win is a pretty versatile cartridge, and I agree the larger expanded frontal diameter is a noticeable difference in animal reaction at impact. IMO, yes it's a great choice for a cow. A lead cow will go 500 lbs, not small and the same material makes their flesh and bones as a bull that may weigh another 100-150 lbs. From what is reported here, folks are scared crapless by the smaller is better/all you need mantra to squeeze off a shot from anything larger than a 6mm. Yes, it recoils more but I can't ever recall feeling recoil in the field when I look back on the shot with any rifle from a 243 Win to a 270 Win to a 300 Win or the 35 Whelen/AI.
The 35 Whelen/AI gives even more frontal diameter (.75" expanded frontal diameter across the sharp petals which are like a boat prop making a cavity in the water, only spinning at 180,000 rpm) and similar ballistics to the 338 Win out to 350-400 yds when loaded with modern powders and a 200 TTSX at 2940 fps. Works great for cow elk, bull elk, mule deer and whitetails.