I did my first track day at Rockingham earlier in the year and left the pressures at 26 psi as recommended for my Mk2.5.
On my second stint on track I noticed that the car was tending to drift out more on the corners.
Had a word with the men that know and was told to increase the pressures by 2 psi per wheel for better handling.
The theory being that as the sidewalls get warmer they flex more and traction is lost.
I increased the pressures and the car behaved much better.
Hope this helps.