I wonder if it's a plating issue too. I'm doing my top end - due (I think) to a locating pin failure on the PTO side - basically, a ring moved and broke up and tore into the cylinder, mostly around the exhaust port. Outside of where the broken ring was scrubbing the cylinder wall though, there wasn't much damage to the plating. I don't see anything that would cause the damage to run all the way down the cylinder like you've got; maybe a lack of lubrication could cause that though. Anyway, mine caught me at an equally bad time. My motor's an IS long rod motor, and I contacted them, but they don't have OE pistons (I hear those are hard to find anywhere; I think it was SPI the offer as a substitute) and couldn't do anything for me as far as price (motor was well out of any warranty though).
Meanwhile, I had several guys recommend Wossner pistons. There have been several very knowledgeable sources who swear by only OE pistons, but the locating pin is a weak spot that keeps cropping up (usually on sleds that see long WOT runs), even on the 850. Forged pistons get dumped on for deforming and/or seizing, but I think there are two things behind that. First is that older forged pistons were 2618 aluminum allow, which could tolerate abuse better, but was less rigid and expanded a lot more than cast pistons. Then came 4032 alloy, which is what Wossners are; that adds silicone back to the mix (both standard cast and 4032 are around 12% silicone; 2618 is <1%). It keeps most of the strength of forged, but makes it more rigid and lowers the expansion rate. The downside is some of the brittleness of cast comes back with it. The second issue is cast is still best in terms of expansion rates. So, especially in a situation where you're offering a warranty to people whose idea of a warm-up is letting the engine run long enough get their gloves and goggles on, cast will have the least immediate failures. There are probably other causes of premature failure, but I'm pretty well convinced that most issues with forged pistons are from clearances too tight and/or lack of warm-up. So I'm giving Wossner's a try, but I will add leakdown checks and piston/cylinder inspections to my regular maintenance. I'm not sure I could have caught my problem in time, but I can't say I'd done a thorough check-over.
As mentioned, I do have a long rod setup, and I'm convinced that's the best on the Pro 800. It's a better choice than the "fix kit" taller pistons, but I don't remember the explanation that well, and can't say how much benefit the 800 HO gets. I think the long rod setup is something that could only help, but may not be worth the effort on the HO. The HO seems to need top end work almost as often as the Pro 800, but I don't hear of nearly as many bottom end failures.
