There isn't really a downside to running a big bar on the K11. The only thing I could possibly imagine being mentioned is that the rear end will tend to snap out on you when you pass the critical grip point on the rear, rather than gradually cause the front end to wash out as it does with the standard anti-roll bar. However, setup to whitelines specifications the cars remain very balanced.
Just build up to it until you are used to the way the car behaves and you'll love it! If you've not run anything other than the standard anti-roll bars, you're in for a hell of a suprise.....the difference in handling is quite shocking.
One recommendation is to go for the rose-jointed rear droplinks, the standard ones don't tend to last very long with the increased loads they see from such a big bar.