Hi Geez,
I don't know what your mount is but I was under the impression that the only traffic that the let 'fly' into Turweston over that weekend are helos.
The road bound traffic is pretty horrendous at that time of the year although I believe it is a bit bettern now the A43 is dual carriage way from the M1 to the M40.
I fly out of Turweston on occassions and am pretty local to Silverstone (~10NM) but avoid that bit of the area like the plague over the GP weekend.
FD