It is interesting that you chose steel. I would have used a plastic spacer since it's cheaper and I assume it would bond with the nozzle selector easier. But maybe plastic would have more turbulence?
Honestly, I wouldn't replace the 1x nozzle, which I measured as 1.5x, and especially with a 5x. You won't see much of a difference between 5x and the stock 4x. The 1.5x nozzle will come in handy every once in a while when you run low on water, especially if you end up coming to a long all day war. Well, maybe it might be ok; but I think ideally you'd just add an 8.5x nozzle or something around that rather than a 10x and a 5x nozzle. Ideally for me I'd use 1.5x, 4x, 8.5x, and shower.