That's for the season, not just May. David has a .348 OBP and is slugging .581.
That demanded a little more research, which revealed that among designated hitters with at least 150 plate appearances this season, Ortiz has the highest OPS. His 11 home runs trail only Vladimir Guerrero of Texas, who has 12. Ortiz is third with 31 RBIs.
It's unrealistic to suggest Ortiz will continue at the pace he had in May. But it's not unrealistic to think he can be one of the top two or three guys at his position for the remainder of the season. Once he got going last season, a much more laborious process than this season, he maintained his swing and was able to stay healthy.
I think whether he hits third or fifth is immaterial. As long as Ortiz is in the middle of the lineup somewhere, he helps guys like Kevin Youkilis and J.D. Drew get better pitches.