If its any help I decided to do a 14 mile practice run a week before my last half as I hadnt had chance to do many long runs in recent weeks and it helps me psychologically to know I can do the distance.
It did tire me but then I deliberately did very little in the week between and got a PB by 2 mins at the half because I was well rested - I think.
I would do the 10 but not push yourself - if that is possible? ie think of it as a good training run.
So much depends on how experienced you are. My son - young - ran a 11 miler on the Thursday before the half on the Sunday - it just suited him - and he was fine at the half. You wouldnt see that in any training programme!