A decent aftermarket exhaust system by itself will add a noticeable amount of extra power and make your bike run better than stock as the factory exhaust is too restrictive.  You won't need any other modifications if you only do the exhaust system.

If you really want your bike to perform better you'll need a decent free flowing air cleaner as well, but if you do that you will also need to re-jet your carby or have your ECU re-programmed (whichever your bike is fitted with) as the bike will run too lean without it and you could burn your valves. 

Tmode.

You can add the pipes, won't get you much of any smoothness or power but it will sound better, won't hurt anything. But, unless you are lucky, only a tuning kit or hiring a tuner will give you smooth regardless of exhaust or intake.

I have Berms. Had them on my ST Custom . They look and sound great.

They are what I had Berms and they do look and sound great

Simple set of slip ons will liven things up for you 300%.

- Order from states will cost you under $300 delivered for your choice of any pipes.
- You can install youself in 20 mins.
- You will be very happy with the extra sound/power.

Cheap enough you can upgrade in a year if you feel the need and start looking at options or asking ppl in the know like OzR above.