The Attitude Shift has a relatively high RG for a true "heavy oil" ball in my opinion.  It's good for opening up the backend when there's some oil out there, but it won't shine on a truly heavy oil condition where you need the ball to rev up in a hurry and roll rather than hook.  A sanded Special or Secret Agent would probably be better in those conditions.  I don't know enough about the Rotogrip Cell to comment on it for heavy oil, though it looks to be an absolute beast on moderately heavy conditions.