My son was tested in our school district. He had a PIAT-R test and had to score 98% or above. He did so then they tested him with the WISC-IV. Overall he had a 121 FSIQ, but in our district he made the gifted program, because he had to have a 130 or above on ONE of the tests. He had a 130 on VCI only. I was told his FSIQ was brought way down due to problem with processing speed (he has lazy eye which causes vision problems). His GAI equivalent is 126 FSIQ.
He probably would be even higher without the vision perception problems. Our neighboring school district requires a FSIQ of 124 which is lower overall, but would not take him since he is only 121 FSIQ, even though he is gifted in VCI. At least our school district uses just one (out of 3) gifted score, even though it has to be a higher score to qualify him for the gifted program (130).
This is an interesting article for you to read:

http://www.gifteddevelopment.com/About_GDC/whoaregiftd.htm

also:
http://www.nagc.org/index.aspx?id=2455

There are some others too, but Pearson's says that FSIQ is brought down by processing speed and working memory and therefore on WISC-IV to use only the VCI and PRI to decided giftedness especially if there is a huge discrepancy between processing speed/working memory and VCI/PRI.

Here is the worksheet for the General Ability Index for the WISC-IV:

http://www.docstoc.com/docs/6546776/WISC-IV-General-Ability-Index-(GAI)-Worksheet

If I think of any other articles I will let you know.