I looked at the Speedway axles and didn't see an upgrade for the king pin. Looking at their spindles I do. If you were to purchase the complete axle kit, it is already engineered and ready to assemble and put on. No need for the upgrade there. They are really helpful over the phone on their tech line. Might be a good question for them too.
Can't imagine how different kingpins make it steer easier? It's already equipped with a thrust bearing under the axle on the kingpin, which makes it turn easy. Did they tell you what is in this upgrade kit? Better be something really special for an extra $150!
They're just needle bearings instead of bushings. I wouldn't use them. They are fine for while turning but when going straight and hitting bumps, the kingpin gets pounded by the narrow lines if pressure from the individual needles. Large trucks still use bushings.
The deluxe will hold up as long as the pins are case harden, but you have about an 85% less contact area at the point of contact between the needle and the pin, less drag..... buttttt will that change the way the load is applied to the knuckles cast bushing housing causing failure due to pressure being applied to a much smaller surface area i.e. load distribution, I dont think that the bearing cage will make up for it, but i may be wrong, it needs more science. but its a gasser so are you going road racing I think not