My Advice: Take Step II of the COMLEX CK exam after core, strong internal medicine and OB-GYN rotations. Also, review Savarese from back-to-front-to-back until your eyes bleed as the new, unannounced recent testing changes have increased the difficulty of questions.
Also, consider utilizing a question bank other than USMLEWorld, which is otherwise great, such as combank or comquest, as they have the nebulous stuff that's more applicable for COMLEX II CK.