Hi BBDad - I cannot speak directly to the bilingualism aspect, but I have a couple of comments.
Our DS5(tomorrow!) has only known English, but his verbal is much stronger than his math. I would bet that most gifted kids have a stronger area, even if they do well across the board. So it's possible that your son will always be stronger in math.
And I think DYS accepts results other than full scale (verbal or nonverbal or FSIQ; reading, math, or total for achievement).
We had our DS tested on SB-V at age 4.1, and it has helped us in planning and advocacy to have this information. I know that after thinking about getting him tested, it would have been impossible for me to wait 2 years! Ask your gut, I guess. If you think it would be useful to have the information now, go for it. If you have loads of extra money, have him tested now, then again in 2 years and you can see for yourself if the second language was a barrier.
