So I have a 09 xt660z I have kevs fuel and o2 mods and a dna stage two filter on the way, the question is will I see any noticeable difference in performance by fitting an aftermarket exhaust in which case are there any systems out there that won't obliterate my eardrums and shatter the neighbours windows?
Thanks in advance Rich.

Hey mate, I have a Tenere with the Kev mods & Akrapovic pipes but original foam filter.
Out the box the Akras arn't much louder than stock pipes, but I drilled out the holes I the end of the baffles a bit bigger as with them completely removed was a bit to loud. There was a small gain in performance & bear in mind they still have cat's in.
Most people I believe , if your handy with a welder or know someone who is, tend to cut out the cat's on the original silencer for better gas flow / engine note / fuel economy & performance.

Absolutely the cheapest method of getting a better exhaust.
Somebody who can weld Stainless will do it for about �30 if you do all the cutting out yourself.

See Redbikejohn's page here: http://www.redbikejohn.com/Tenere%20...s%20Review.htm

About halfway down the page is where he shows you how to cut the cat out and drill pipes for better airflow.

This doesn't change the exhaust sound much at idle, only under revs and you'll notice a small difference in the feel of the engine.

It was never that much louder but sounded a lot throatier.

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Bike: 2013 XT660Z, TKC70 tyres

Mods:
Barkbusters, Scottoiler, DIY Tail Mod, DNA Stage 3, Power Commander V & O2 Eliminator, Exan X-Black Stainless exhaust, Tool tube, Ohlins linear front fork springs, Nitron rear shock, JT front and Supersprox rear sprockets, D.I.D. VX 520 chain, Adventure Spec bashplate, DIY USB Outlet, DIY chain guide, Kev's Throttle mod

http://www.facebook.com/onemooseonemotorbike

Thanks for that, looks like the angle grinder might be making an appearance then!