FWIW, you only slow down a rod, past it's designed "speed", if you overLOAD it. IMO overlining and overloading are not the same thing.
i.e. (tapers aside), if you have double the line weight, but throw half the distance, the weight you are throwing is what the rod was weighted for. Not more. It's not overloaded. It's properly loaded. If you did the same cast with the recommended line weight, you'd be underloading it.
I am a proponent of overlining rods that are specialists for small streams where casting will be nearly always fairly short. And FWIW, I'm not sure what people are calling "flipping" here. I do backcast, and more often some sort of hybrid roll/back cast which I call a "snap" cast. Think of it like a backcast but starting the forward cast way too soon, so that the line doesn't actually go behind you. And yes, the line weight makes a difference.
My main small stream rod is a 4/5 wt and I have 2 spools for it. A 5 wt and a 7 wt. The 5 wt gets used for the larger, more open small streams where you might be casting 20+ ft frequently. The 7 wt gets used on the really small, thick spots. That's 2.5 line weights over the rating!!!! I think it helps a lot. Just be aware of what you have on there when you do come to that huge, wide open pool where you can really open up with long casts. Now, yes, that extra line weight becomes a disadvantage.