An internationally known gifted expert that we consulted is very firm that quirks and sensory issues are common, and argued with me a few times over whether DS has SPD or if it's just part of his giftedness. (http://www.sengifted.org/articles_social/Lind_OverexcitabilityAndTheGifted.shtml
A small amount of definitive research and a great deal of naturalistic observation have led to the belief that intensity, sensitivity and overexcitability are primary characteristics of the highly gifted.
DD has OEs, DS has OEs and SPD. DD has anxiety (mostly from being in an inappropriate learning environment and the OEs). DS also has vision issues, written output disorder, some gross/fine motor stuff. He's EG. He has some ASD traits, but is not on the spectrum. He has some pretty interesting scatter in some of his sub-test scores on IQ testing - which is normal among gifted people. He's clearly pretty neurologically different in a number of ways. Oh, and he's awesome.
But to the posters with young kids - it will be okay :). Your kids are so very young, nothing is set. The range of developmentally normal in the preschool set is HUGE, and can be more complicated if a child is gifted. It's great that you're pursuing evals and learning more about how your particular kid works, but don't fret too much - said as a mom who fretted/frets a lot! Your kids may or may not end up complicated, may or may not end up with labels and diagnoses. Entering diagnosis land was scary at first for me, but in the midst of it I still had this great kid to jouney along with.
This is a great read:
Robison self-diagnosed Asperger's as an adult, and he's had a great life - worked for KISS, runs his own specialty garage because he loves cars, on his second marriage (both successful), and raised a child.
Watch a little Big Bang Theory - these are a group of quirky, gifted guys who are doing pretty well. At worst, they'll make you laugh:
Books to read about kids, development and difference:
Webb et al, Misdiagnosis and Dual Diagnosis of Gifted Children and Adults
Eides, The Mislabeled Child - also see their websites
When the Labels Don't Fit