It seems prudent to get DD5year's testing done as well.  I predict that she will score similar to K, because K's scores are temporarily depresssed by the "unwillingness" factor.  A lot of second borns are more easy going, harder to notice, and less weird all around, but no less bright.  
Willl it influence how you treat them?  Well, (wink) I doubt you are overestimating DD5's abilities at this point.  That is human nature to assume "weird" = more gifted.  Reality is a different story.  Remember - you are establishing floors of potiential, not brackets.
Smiles,
Trin