Depends.  Low revs. high speed bowlers in general should get strong cover equipment, but what is he looking for?  Is the ball for heavier, medium, or lighter oil?  You say he has lower revs. but what about his axis tilt?  Does he try to bowl more down and in or does he look for more of an arc?

Assuming he is a down and in bowler (most high speed low rev. guys are) and he is bowling on heavier oil I'd go with the Rogue Cell (actually an original Cell may be better).  For medium to lighter oil the best Roto ball for that shot IMO right now is the Nomad.  For me pearl balls are better suited to open up a shot and lower rev. guys don't get to take advantage of that too much unless they are capable of adding more axis tilt.