Do you mean some sort of electronically controlled, aftermarket HP gear set assembly?
If not, your 850 already has adjustable timing gears (both) but they're set as is from the factory and I wouldn't advise playing with the adjustments unless you're sure that you know what you're doing. It will effect idle quality if altered and what you might gain at the low end, you'll lose at higher rpms or vise versa. The only way it'd be idea for performance is if you could add on something that's electronically controlled, like some modern day HP cars are now from the factory (like some BMWs for example).