Hello
Filippo74 is correct in this, as it is also my experience that just clicking a spot with a brush, the spot tool in LR5 seems just as quick as LR4.
The problem is the painting of a shape that slows the machine to crawl and the fact that the tool stops adding to the shape as one continues to paint.
The masking brush which is also a painting mechanism is very good and does not cause problems. What I cannot really see what the actual difference is. Both the masking and the spot tool make a vector path with a bitmap fill. The mask tool protects a portion of the image using a red mask ro show where it is, and the clone tool samples another part of the image for its fill.
yet the spot tool in its painting mode is really crude.
Mike Engles