When we bought it last winter, 535 was the largest Case IH available here. I think there was a 575 Challenger, but we didn't want a 2 track machine again. And the 510 hp version I demo'd seemed overrated, it couldn't outpull my old 9400T(425 hp).
There is a small mfg company in Hudson Iowa called Holmes Welding that has been converting 611 motor scrapers to dolly wheel scrapers We got one last week and it is a nice outfitt. I guess the 611 was a shortlived idea that cat had for the small contractors and most of them have been converted to water wagons leaving a nice pan for converting. It weighs in at 32800 and works great behind a 6R think they were rated at 11yd struck and 16 heaped could add some greedly boards and have a nice replacment for 435. They are new enough that parts are still avalible. They have some other products that are pretty neat some pull type 30 ton dump wagons ejecton bodys and box rollers. They also had a cat 660 motor scraper cut up and mounted with a fith wheel to a cat 740 artic for PCI looked pretty cool. The website is www.holmeswelding.com