with your design, the front wheel is true caster, the wheel axle is behind the steering axis.
the OP’s design the front wheel axle is in front of the steering axis.
So are they still both technically called caster boards?
I think the first time I’ve heard it described as a caster board was on this thread. I really like the slick steering design on the SpeedBoard, but I strongly suspect it’s less stable. You’re right that my steering does use a traditional caster.
You mention that the Speedboard has its axle in front of the steering axis, but that’s not really quite right. The axle is in front of the attach points, but the steering axis on the Speedboard is virtual - and not stationary. That’s actually the reason I opted for a traditional caster in the end.
In the coming days (weeks?) I plan to rework my steering frame. Mostly the plan is to put the stationary portion of the frame inside the pivoting portion rather than outside. This should get rid of fair bit of the bulk and improve the clearance, without changing the steering at all.
Today I did a medium speed test ride. I don’t yet have the bluetooth dashboard setup for this board, but I think I was right around 20 mph (based on my other board). This one is designed to have a top speed right around 30 mph. I’m pretty sure I was well below that. In any event, the steering felt rock solid.