We had my DS5.5 tested at age 4 years 9 months on the SB-5. (We started looking at aroud 4 Years 4 months but waited the extra 5 months--I wanted to continue my GT denial for as long as possible)
We definitly had a lot of your same concerns about our son and the IQ testing gave us many insights into our son and his learning abilities. Out test included the actual IQ test and some informal assessments. We got the raw scores as well as a 5 page write up. I think you also need to find a tester who has experience with GT kids.
We did eventually follow up with some acheivement testing at 5 years 1 month but that was just to qualify for the DYS program. I honestly don't think I would do the achievment test on a child age 5 and younger unless there was a real need (school placement, program qualification, etc).
