We have a sneaky DD5 too . . . seems like a perfectly average, happy-go-lucky little girl with no particular aptitude for much . . . and happened to score 148 on her WPPSI.

She's perfectly happy in her non-gifted K class, making friends. Just keeping a close eye out for boredom/etc.

I think you should test sooner rather than later. Nobody here on this board has any idea what "average" looks like, and we compare siblings to the most "obviously" brilliant child.