Well, I've been trying for literally hours & hours & hours to find the one lineup that I know I could beat, but I'm starting to get frustrated and I just worked out the probability of finding it.
There's 15 possible rides for the AI, the same car never appears in a lineup twice, so the probability of getting the right 5 cars out of 15 is something like:-
( 1/15 x 1/14 / x 1/13 x 1/12 / x 1/11) = 1 in 360,360!
So if I sit here for days on end I may find it, but I'm ready to give up, so I'll share the info for anyone else who wants to try and can get lucky. I've based the fact that I think they can be beaten based on the AI's pit strategy for each car in the field which I've researched and posted in a thread in the race reports forum. (its also included as a link in the GT4 FAQ stickied thread.)
Anyway, the race, weapon of choice and lineup required is as follows and should give a storming 200pt race.
Tsukuba 9hr Endurance.
Car: Renault 5 Turbo '80 (0.0mile prizecar, oil changed, S2 tyres) / MR / 168HP / 970kg / 5.8kg/HP
Lineup to look for:-
Alfa Romeo 147 GTA '02, Alfa Romeo GT 3.2 V6 24V '04, BMW 330i '05, Audi A3 3.2 quattro '03, Subaru Legacy B4 2.0GT '03.
Needs to have Subaru starting 5th and one of the Alfas on pole. The Subaru is quick on warm tyres but pits around 19 or 20 laps, the Alfas are no contest but block the other cars well! I've had several aborted attempts to find out every cars strategy and can get 23 good laps out of a set of S2 tyres, and only 26 out of S1s.
I was able to lap in the low 1'07s to high 1'06s on S2s.
Good luck to anyone who finds that lineup and wants to give it a shot.