Kubotas B2710, M6800, L6060 cab, Volvo EC excavator, 2 ZTRs and various implements.
I have an older B2710 with hydrostat and have used a 6 if not 7 foot blade on it. The limiting factor was traction. Have used it a good bit with 6 foot landscaping rake pulling a good bit of dirt with never an issue. Just don't use in higher range than you should for load.
Actually, I would get a 60" blade for that tractor if you have a choice. It will cover your tracks better when angled, and have a bit more reach for ditches, etc.