Thanks Mich and Mum0405 for your replies.

My DS was tested on the SB-V so I'm not familiar with the WISC.
His cognitive profile on the SB-V was extremely even (all subtests at or near celings) with very little between the Verbal and Non-verbal, so clearly that didn't tell us anything except that he's smart!

Reasons I think something may be going on?
Hard to put my finger on! He's our eldest so some of this is hindsight. His language acquisition was different to our other two children but we only noticed this after we'd had the other two. DS8 had a massive single word vocab before he started putting words togther much at all(around age 2). At the time this didn't seem "delayed". We'd taught him baby signing and he could communicate fine so it wasn't an issue. It was only when we had our next child (DS6) and I thought he was delayed because he seemed to have comparatively few words, but then started talking in complex sentences very quickly (as did No3, DD4)at aroud 12-18 months.

Now at 8, he substitutes "you know" and "thingy" with a shrug and a look to me instead of actually naming and explaining things.
He seems to frustrate his teacher at school because he's bad at "self-reflection" and reacts badly to situations by getting frustrated instead of "using his words".
I actually did a google search on CAPD and verbal expression" before I read your thread, because it ocurred to me that he's actually having trouble getting out what's in his head.

I'm going to try and find a Speech Therapist experienced with Gifted Kids and have him evaluated, as the problem is that he probably seems pretty normal for a regular 8yr old but he's not a regular 8yr old.

Like your DS Mom0405, academically he's doing fine, having been accelerated but I just feel there's something going on (oh, I forgot to mention that getting him to write is getting blood out of a stone!).
Cheers
abra