I am looking at getting a set of wheels for trackdays and was wondering what would be a good tyre choice, rims are 205 40 r17

Id get the smallest possible diameter wheels for the track.

As for tyres, if you dont aim to drive the car to the track days i'd shod it with avon slicks but for something road legal Avon ACB10's are about as gripy as you'll get.

where's the best place to get ACB10's or Yokohama's

BTW are the ACB 10'S not reported to be a bit hairy in the wet?

I'm sure I saw it on here that yoko's were a better allrounder?

if your gonna run ACB's you'd need to make some susspension adjustments, ide by some "ex racer" yoko's or the like