In P. O. Ackley's manuals he does not recommend going over 5% more than the max load for a non-improved cartridge.
I have two, 25-06 imp. and 30-30 imp.
They are not any harder to load if you buy the dies for the improved cartridge.
In my experiance you need to keep the chamber on the tight side of spec.
If you want to have fun, go for it. It's no differant than people hot rodding cars. But in reality there are other cartridges that will do the same thing as a 260 imp.