I hear you. I did look at the sample tests, and I don't think the 2/3rd is a good fit. I may try the sample test with him, but I don't think it's challenging enough. I thought the 6th grade test would be hard, and he sure wouldn't get them all right! But he would just as surely get some right. So maybe the 4/5th is the best fit.
I fear I oversold the speed aspect with DS7.

Now I fear you all think he's got some LD that makes him incapable of taking a test. Not so!
He's deliberate, not incapable of functioning. Think Spock, not incapacitation.
He did fine on the WISC, even the timed tests. There's a big difference between a timed test of nothing but math facts and a test that happens to be timed that asks challenging questions. Besides, this is for no purpose but my own information. We're not competing for anything. I just would like to know where he is operating right now. If he got zeros on the test, we'd be out nothing but money...unless NUMATS and CTY share info about the kids. Then it's a bigger issue!
P.S. DS7 is on a math bender lately, which is also a factor for me that I didn't mention. He's leaping ahead faster than I can believe, so while he's probably not doing middle school work in its entirety today, I'm trying to forecast what he'll be doing by test-time.