besides the weight reduction and stiffness?

what gains do i get with a gsxr swingarm and is it worth the trouble?

benefit is wider tire.  that's really about it.  maybe a cooler looking sprocket.

you will probably have to mill it where it enters the frame (make it smaller) and shim the sprocket to be in line with your tranny sprocket...  find brakes..  make/setup new dogbones to acquire the correct height