I am having issues with the '3 layout' version of this track and went searching for a decent version. Finally found one in the Triple7 racing BTCC season mod pack. AI works, track map works and there's only 1 or 2 spots you can fall off the map unlike the other version.
I've been running it with 0 fps issues with 16ai cars.
Here it is uploaded to my aussie VPS -
http://games.xrst.net.au/assetto/oulton_park%20v1.1.rar Roughly 500mb for the kn5 file, compared to 360mb for the other one.
If people could give it a go and report back whether it's better or worse and maybe we can use it instead of the problematic one.