I'd go with the WISC - V which is rumored to be coming out soon, or the WISC IV, because they are the most familiar to people who are doing the interpreting. I'd also be sure to get an achievement test, ideally a MAP test so you can really see what he knows and what he is ready to learn. Be sure your tester can calculate a GAI, and find out in advance how much spread there has to be before the tester will say 'No FSIQ can be measured.' This is really important because you are much better off with that than a average that misleads folks into thinking you child isn't gifted if they are.
For kids with 2Es, there may never be a single number from an IQ test that show if they are gifted or not. Seeing the spread of the subscores and their pattern can be much more useful.
You should retest. Hopefully with a tester who is quite experienced with kids with AS who are gifted, such as
http://www.davincilearning.org/www.amendpsych.com/or
www.grcne.com/I'd say that this is worth traveling. And get the sibling tested while you are at it so you have some frame of reference.
Smiles,
Grinity
Love and More Love,
Grinity