I'm speaking out of school here as I'm a month or more away from firing up my 836cc motor. However, I will say that Wiseco, the manufacturer of the 836cc kit I own, makes quality products and I wouldn't be concerned on that front.
More broadly speaking on the topic of adding capacity to an engine, its one of the ways you can make more horsepower and torque. All things being equal, increasing displacement increases the work the engine is capable of. Should you choose to go the 836cc route, I would recommend Mike Rieck's help with porting -- as the stock heads don't flow sufficiently well to make good use of the added cubes.
