As I mentioned over on Chastity Forums, I have a Steelworxx Steelheart coming!
I agonized over the total length, but after going back and forth with Steelworxx, I settled on 85mm, which will be a little longer than the troublesome CB-6000s that I currently wear on and off. What finally convinced me to go shorter rather than longer was Dev's observation that you're flaccid most of the time, so why optimize for comfort when erect? It made sense, but it contradicted with Thumper's sizing of his own Steelheart (though I know he's currently thinking of a smaller tube -- the question is how much smaller) so I was/am a tad worry.
In the end I went for 85mm total length, 35mm tube diameter, both a 42 and 45mm A ring, the comfort ring on the tube, the integrated lock ... and the PA fixing. I considered the 40mm ring, but it just looked too damn small. Seeing as how I'm currently bouncing between 1 3/4" and 1 7/8" with the CB-6000s, 42mm seemed much more likely.
I'm crossing my fingers that metal will be much more comfortable. And I'm totally jumping the gun on the PA fixing, seeing that I don't have a PA yet. But now I have to get one. I keep putting it off for some stupid reason.