You guys are being awfully conservative! A 250 is a 7 main bearing engine with a relatively short stroke. You can turn it WAY up, but with most cam and carb combinations there is no reason to turn it up past 5000, or for that matter the above mentioned 4200 is maximum horsepower with a cam profile of around 200 degrees @ .050.
The point is if you want to run a bit lumpier cam with a good solid stock bottom end you can. I don't think you would get into any trouble unless you stuck a hot cam in an older engine, and started turing it up real high without replacing the rod and main bearings and making sure the crank is in good shape.
