Micron-VERY similar in sound to SATO. Deep growl-very muscular.
Akra- Deep, a little softer than the Micron, deep softer tone.
2Bros- Loud, cruddy, but loud. (basically straight 2" pipe with BS baffles)
Those are the kits I have personally owned. The only one that was standard mount was the Akra, Micron isn't made anymore but is still available. I haven't yet heard an RC with GPR and they are readily available as are the Yosh's.
2001 #62. Ohlins rear/valves, Micron high mount, HyperPro damper, SharkSkinz, Tyga billet triple clamp, Tyga Carbon Fiber fender and hugger, Ti bolt/custom subframe/alien motion 8 cell diet, 15/41 520, COP conv. PCIII, Venhill lines, modified air box, turn signals in headlights...<deep breath> ZG Touring windscreen, Tech G rear sets, CRF450 rear master w/HRC cover, Tokico 6 pots w/V-pads, CRG Bar end mirrors, PSR Shorty levers-use only clutch, wanna-be basic racer paint, Roman Gold PC wheels