In all acuality, a slightly modded saw should outlive a stock one, as it will run cooler. The longgevity issues come from opening the ports to extremes, it wears the rings faster. The highr RPM is a toss up, the motor breathes better, flows better and is happier, so it shouldn't affect life of the saw much?
The increased production is well worth it!! Going from seeing a stock saw, to running a fully modded saw there is no comparison! The biggest complaint I have with the 046 is fuel usage. With the BB kit it is thirsty!!! I can empty a tank in 15-20 min. depending what I am cutting. But I can cut twice as much wood in that time as well. (Comparing my 350 to the 046) The only saw I now own that isn't modded is my old 350, its my backup, and I don't want to mess with old reliable, saved my butt to many times!!
I would encourage anyone to mod thier saws, at least muffler mod them, it just makes the saw happier!