For me, the easiest of them was the Peugeot, which I always knew was a natural drift master at this circuit in the wet. A quick recce showed that the most effective mod was a stage 3 turbo: I couldn't catch it with full race suspenders or a VCD, which I thought might help, but which only made the car unstable on entry. I could still apply full power, even with 439bhp on tap. What was absolutely critical was the line you took, and my fastest laps were those with a late entry, turning at a point where you can more or less straight-line the exit, particularly on the last bend. Indeed one of my fastest laps (which I didn't count) was one where on both of the last 2 corners, I actually went off on the outside of the bend and was accelerating hard from the moment I hit tarmac again. Once I'd tidied that up, I went even quicker...
The Ruf was a more delicate affair: I went for semi-racing suspension as the mod as more power was counter productive. I had high hopes for the Ruf here, as I felt it was driveable enough to beat both of the top supercars, and if it wasn't for l2ev's delicacy with the Ford GT, it might well have done. It had good traction, and could take full power in 3rd, which was a blessing because the torquey motor gave good acceleration from about 4000rpm. In 2nd you needed to hold back a tad and it was always a toss-up as to which gear you wanted at any one time. Usually 2nd won out, but sometimes 3rd proved a touch better.
The Caterham on the other hand was a nightmare. Wheelspin everywhere, and somehow it was quite difficult to detect, something to do with the high gearing I think. Usually I'd end up coming out of the hairpins in 3rd (equivalent to 4th in most cars beacause of the high gearing) with zero acceleration. If you lifted off, you had the bizarre experience of having the revs go down, while the speed went up!

Even after all the practice I got in the Ruf, I could not improve on the 1'17" I got early on
Sure, the Caterham was frustrating, but in the right car, this proved to be a very rewarding track. I hope everyone else found the same!