Never tried a Whidden. What noticable differences are you seeing? Enough to do anything for you down range? Or just for piece of mind?. In my post I wrote RCBS but meant Redding. Was traveling and don't know why. Lack of sleep. But I see really good results with half inch 5 round groups on magnums when reloading with Redding dies. I have been using a full size Redding with 336 bushing and can't think of a reason to change . Don't know if I'll get better then that on factory AI and Cadex rifles.
I get a lot more shoulder bump variation using a Redding Type S FL sizer vs the Whidden FL bushing sizer. Mind you, my experience with this has been with 6.5 creedmoor, as I had FL sizers in this cartridge from both companies. Same press, same lube, same brass, same press technique - but more repeatable and precise results with the Whidden. It has caused me to move to Whidden for all my cartridges.
Shoulder bump variations will change the pressure and and thus velocities - an inconsistency in ES/SD will be seen. The greater the variation, the greater the inconsistency.
What's interesting, is that PRS precision rifle shooters seem to not like Whidden dies as they supposedly see more run out from them. I see this posted on PRS/precision rifle Facebook groups (ugh) and here. However, bench rest shooters, such as those on accurateshooter.com, swear by Whidden and think they are some of the best dies - this group of shooters is trying to achieve the goal of ultimate precision.
I've never measured run out, so I can't personally speak to that. What I can say though, is that my most accurate reloaded rounds to date have all been produced with Whidden dies. All of the cartridges I currently reload for have an ES of 15 or less (a lot more factors than just the dies for that, I know), and my smallest groups ever shot were produced by ammo reloaded with Whidden dies.
For me, I have seen a difference and have great success with Whidden dies. However, if something else is working for you, keep using it.