Alexander, I often use my 9' med/stiff action 4 wt for beach fishing, if the wind isn't up, and if the flies I'm using are small enough. The lighter rod allows for the sub-14" fish to feel like you have a good fish on the line, and feels much better matched to fighting searun cutthroat than my 6 wt, which often feels like overkill. However, my 6 wt is better for casting larger baitfish patterns, coneheads, etc, and casting in the wind.
But I prefer using my 4 wt, whenever I can. It does not overly stress out the fish if you use at least 3x tippet and know how to "put the wood" (use your butt section) to a larger fish.
I am now thinking that a med/stiff 5 wt would be about the right compromise for beach fishing for searun cutthroat.