Think of it this way, the purpose of porting is to flow more air and fuel into the combustion chamber to produce more hp and torque. This is done in two ways. One is to smooth out the flow and make minor improvements in power at the same rpm, the other is to change the port duration so that the engine will opperate at higher rpm which will show the greatest gains in power.
Now, with your engine producing more power, and running at higher rpm, the loads on the bearings and rod are increased. If you increase the loads on those parts, they will wear out faster. You'll also burn more fuel for the added power. If someone claims their modded saw will last as long as a factory saw, either they haven't increased the saws performance, or they are falsly claiming that the mods won't wear out the saw faster. There is no free lunch.
A properly modded saw will cut faster, so that is the performance you are paying for. Time is money, so it is worth considering modding a working saw, or getting a larger cc saw. The disadvantage of the larger saw is it's heavier and wears the operator out faster.