As great as they are, the Thunder can't really defend as a team against a disciplined offense. Guys like Ibaka are great weak side defenders but you'll often see guys put up big numbers on him (good shot blocker rarely equates to being a good interior defender). I don't think it's quite their time yet. Almost certainly next year, but not yet.
The Thunder's lack of offensive discipline will see them come undone against this Spurs team. They run the most isolation plays out of any team in the league by a wide margin, which is fine since they have three fantastic scorers in Harden, Westbrook and Durant. Unfortunately, that will only get you so far in the grind of the playoffs. The two teams they've played so far: Dallas & LA were both old and extremely unstable as a unit, surrounded by turmoil and imploding under controversy.
Either way, the Thunder & Spurs are the two best teams in the league this year, and it should be a great series.
I say Spurs in 6. Then Spurs sweep the final.
But no matter who wins, this WC Final is for the championship.
The East is full of hard-fighting teams that are built on defense and team-first concepts but downright struggle to put points on the board. I don't think the Spurs will have trouble with any of them this time around (ie. the eliminated Chicago, Philly, Indiana, Miami)