I would not trade the #3 pick for Okafor. Okafor had a bad rookie season by every metric except points per game.
-Okafor's advanced stats were poor. Due to his inefficiency and poor AST:TOV ratio, he only managed 0.3 offensive winshares on the year-- an exceedingly bad number for a supposedly offensive minded big man-- and he posted a VORP of -0.8. For contrast, even Marcus Smart managed 0.7 OWS his rookie year, and he managed an excellent 1.4 VORP on the back of his outstanding defensive stats.
-By all accounts, Okafor was either a bad defender or a terrible one. He looks like a disaster in the PnR, and you can bet that in the playoffs, opposing teams are going to gameplan for him. He doesn't show much motivation on that end, so there is no reason to believe that he will improve. One-way offensive centers need to be extremely good on offense to make up for their D, especially when they also don't shoot 3's.
-Finally, Okafor only managed a 12.8TRB%, which unfortunately compares with Olynyk's career mark (12.4%). Typically, a center will collect over 15% of available rebounds. Moreover, rebounding does not tend to improve with age, so it's unlikely that Okafor will ever be close to an average rebounder. This is especially bad for a team that hangs its hat on defense and that likes to play small.