I've been running Ironman sprockets front and rear on my WR250R for the past couple of seasons, and can vouch that the rear sprockets are extraordinarily durable and lightweight, being made of case-hardened tool steel and finished in hard chrome or PVD zirconium coatings. I can't see choosing a different rear sprocket any time soon, as the ones I've run for 10,000km+ show hardly any wear and could be mistaken as brand new unless inspected very closely.
Front sprockets take a lot more abuse though, having fewer teeth to distribute the load and presenting more acute angles (and suboptimal forces) to the chain links, and running at higher RPMs compared to the rear sprocket. Here's a view of a 13T Ironman sprocket after about 7,000km (one season) of muddy, gritty riding thanks to an unusually wet year (bottom). For comparison is a new Renthal 13T sprocket (top).
As you can see, the Ironman shows mild signs of shark-finning on the teeth--totally expected given how crappy the conditions were that I ran this in. The chain (a Regina 520) was also replaced at the same time as the sprocket and barely looks broken in. So the sprocket absorbed most of the abuse, as expected.
I would consider this acceptable wear, especially given the extreme wet conditions it was exposed to. Nevertheless, I wanted to compare how a Renthal sprocket holds up, given they're cheaper and easier for me to obtain. The Renthal shows good machining and also appears to also use a case-hardened tool steel, although I don't have a reliable means to test that. Interestingly, the Renthal's tooth profile is different from the Ironman, and incorporates a scallop on the front which may aid in reducing wear or noise. This pic shows the Renthal on top of the Ironman, with the Renthal having teeth with a more triangular shape and pointed top.
Having run the Renthal now for only a couple of hours on the road, I don't notice any differences in noise or feel, but then I wouldn't expect to given a mere seat-of-the-pants assessment.
Will compare results after another 7,000km. Hopefully it's a drier season this year, even if that means unfairly favoring the Renthal.