Thanks wimbles - yes, indeed - we were told he’d scored very highly indeed in our chat with Mr K 
catchmum, be positive - my DS2 was definitely not borderline!
mum, we sold the 10+ to DS1 along the lines of:
if he sat it, he’d only have to do 2 exams (W & T) whereas if he waited for 11+ he’d have to do W, T, the Sutton Grammars, and maybe Caterham. And also SATS (we somehow forgot to mention all the end of year exams at T, though...)
We pointed out that most of his friends wouldn’t be going on to the same school as him anyway (state primary - probably >75% go onto the local comp) and even if they did, the chances of being in the same class were slim.
Plus of course we highlighted all the cool stuff he would be doing at T.
He LOVED the Junior year last year, and is so glad that he didn’t stay at his primary for Y6.