Based on "game score" (basically a single-game PER approximator) that was by far his best game--game score of 44.3; he only had one other game that season over 30 (31.3 in the OT loss to the clips).
Outside of that PHX game, his four highest GmSc games actually have come this season, three of them in a two-week span between the Christmas game against Denver (41pt, 6reb, 4ast, 16-26 FG, 3-6 3P, 6-6 FT, Gmsc 32.4), and the Laker win (32pt, 5reb, 6ast, 9-11FG, 13-14FT, Gmsc 33.0). For the Houston game referenced below, his game score was only 31.4, which would rank 6th thus far in his career.
That's the best game because it happened in the playoffs with the possibility of an 0-2 hole breathing down our neck. Also- after that game, Ron Artest that Roy was the best player he's ever played against.
The Houston game probably tops the Phoenix game (IMO) because Roy did it against a VERY good defensive team in Houston, in the playoffs. He did it with two of the better wing defenders in the league draped all over him the entire game.
On the other hand, Phoenix never bothered to play any defense.