The 519a 4500K is nice, but the 219a sw4500k is special.
I think the 519a is more versatile as it's more efficient and is easily and cleanly dedomed.
I currently have one light with a 519a 4500K, used it stock for a while then dedomed it. Now it's close to 3000K with a peachy tint.
I've read that the 5700K dedomes to around 4500K and below the BBL, never tried one to compare to an sw45k. Apparently they are really pink.
My thoughts are that it would be hard to beat the sw45k for my tastes.
One thing worth mentioning is that depending on specs (efficiency bin) I've noticed that some sw45k are more pink than others. I like the strong pink ones.
Things like AR coatings on lenses and reflectors can all have different effects on tint also.