you will notice more difference in changeing sprockets or even flywheel weights. on most modern bikes there is not a hole lot to gain in pipes, the factory spends a lot of $$ on them.
a good chunk of riders will not notice the power difference with pipes
but they do look cool and sound awsome. if you were looking to replace it you may want to look for a "used" stock pipe, they are much thicker than aftermarket, leading to less dents in return giving you better performence
i do not know a whole lot on 2 stroke pipes, mun knows a lot
~steve