ESPN has ratings by position of NBA players using Hollinger's "value added," or VORP (Value Over Replacement Player). The definition appears at the bottom.
Using these ratings:
Aldridge ranks #2 of 77 PF
Lillard ranks #4 of 71 PG
Matthews ranks #6 of 68 PG
Batum ranks #6 of 61 SF
Lopez ranks #15 of 52 C
So your can see that four our starting five are in the top 10% of players at their position in the league. No wonder our record is so good. (One caveat is that this metric is PER-based, which measures offensive productivity. Defense might be a different story.
Value Added - the estimated number of points a player adds to a team’s season total above what a 'replacement player' (for instance, the 12th man on the roster) would produce. Value Added = ([Minutes * (PER - PRL)] / 67). PRL (Position Replacement Level) = 11.5 for power forwards, 11.0 for point guards, 10.6 for centers, 10.5 for shooting guards and small forwards
The power forward ratings are at: