Yamaha Exhaust Pipe Modifications

I'm looking to upgrade my Yamaha bike's exhaust system and I wanted to see what kind of modifications others have done. Specifically interested in hearing about performance increases and how they handled fitment issues with different bikes models (FZ6R, FJR1300, etc). Also curious to know if anyone has experience with custom exhaust systems that don't void the warranty. Looking for advice on best brands or aftermarket parts to consider, as well as any common pitfalls to avoid during the installation process.