Well, you probably already know there are several 'iq' tests on the web, some probably less accurate than others. I think it is a valid point to want to pursue, however I am not sure of a great test for adults and that would probably cost a bit of money.
To make a better decision on testing, you might want to visit a site like Mensa, to see what tests they except, or hoagiesgifted.org to just look at the list of tests there.
Alternately, you might want to review 'gifted' characteristics lists, this might reveal more anyway. There is a good one for adults here:
Gifted Development Center - Info for Adults Good luck!
