Highest proposed scoreExtension on Roland's answer:
There are unconfirmed reports that a 2069 point play was found in 1982 by Josepha Heifez Byrne using sesquioxidizing.
NOTE: These hypothetical records were established before the introduction of OSPD 4 and have not been update for OSPD 4.
Highest Single Play
1,778 points: OXYPHENBUTAZONE, found by Dan Stock (OH) in 1996
Other words formed were (O)PACIFYING, (Y)ELKS, (P)REInTERVIEWED, (B)RAINWASHING, (A)MELIORATIVE, (Z)ARFS, and (E)JACULATING.
SOW PODS record
1,790 points, BENZOXYCAMPHORS
Highest Single Play Using Any Dictionary
2,069 points?, SESQUIOXIDIZING, found by Josepha Heifetz Byrne (CA)
Byrne found this play in 1982 using words from unabridged dictionaries. The word itself is from her own book Mrs. Byrne's Dictionary of Unusual, Obscure, and Preposterous Words The word isn't found in that form in any standard unabridged dictionary, though the OED lists SESQUIOXIDIZED and SEXQUIOXIDIZATION.
If we only allow words that actually do appear in standard dictionaries, then BENZOXYCAMPHORS for 1,962 points - found by Darryl Francis, Jeff Grant, and Ron Jerome c1986 may be the record.
From this source pg. 68.
However I do not think that this can really be considered a puzzle then, since it's more just trivia.