No no no no no. You MUST A-Spec this event. It was one of the only championships where I A-Speced the whole thing. I used the FGT (F1) and without A-Speccing, the race becomes a real worry.
Here's my evidence on why you must A-Spec this event;
When I gave this my first attempt (Toyota Minolta at full tuning) in B-Spec, the FGT's were a lot faster, due to weight and downforce and tyre ware.
I gave it a second attempt in the FGT. (B-Spec again) During the first race, which I beleive is the Tokyo race, my lead was reasonable. It was close to 20 seconds and I was sure I was going to win, but because of the different settings you can place B-Spec on, I had to pit one extra time before finishing the race, which lead to me losing by 3 seconds.
My third and final attempt I decided to go all out and give up my whole weekend just to A-Spec the event, and what a difference it made. I was going 5-6 laps longer then the AI were in most of the races (except the 'burg) and even 10-15 laps longer then the AI around Super Speedway. Having this extra 5-6 lap advantage is great, because you can then use simple maths to calculate pit stops for yourself and for the AI. As well as having your own technique, you can get a further lead then a lap (If you lap the AI) which means that with every pit stop you are increasing your lead bit by bit. Sure the races take an hour or so to complete but man is it worth it. You get to learn tracks that you may or may not like, you get an amazing car (Sauber) and you get the fulfillment of going 'I raced that, and won. Im awesome'
B-Spec from my findings is a waste of time, and unless you are certain you can win the race because your car is over-powered, you find yourself checking on it every 5 minutes which means that the whole point of the game racing for you goes down the drain.