I really enjoyed these B-spec seasonals. The most fun I've had with B-spec since the early days when I was first training my Bob's.
I used a stock BMW 120 '04, with Stage 1 weight reduction to put it on exactly 400pp. My Bob took the lead on the 4th lap, with just a little prodding from me to overtake the lead car.
For the 500pp race, I used a fully tuned Dome Zero Concept '78 which came in at 515pp, so I limited the power to 87.5% to bring the pp down to the entry requirements. Just like the first race, my Bob made his way upto 2nd place easy enough, but again needed prompting from me to take the lead on the 4th lap.
Finally the 650pp race which was where I had the most fun. I used a Nissan Fairlady Z Concept LM Race Car. Fully tuned, it came in at 653pp, so I limited the power to 98% to bring it down to 650pp. This race was a decent challenge and needed constant prompting from me for my Bob to move up the field. The lead car was a Ford GT LM Race Car Spec II which built up quite a big lead. It was lap 6 by the the time I'd worked my Bob up into 2nd place, and the Ford GT was 6 seconds ahead. Fortunately it's driver was on a downward slump and wasn't lapping as quick, so I was able to gradually catch him over the next couple of laps, and then pass him on the start/finish straight just as lap 9 began. The Ford GTs best lap time was 7 seconds faster than my Bob's best lap, so it may be trickier to win if there are 2 decent front running cars to push each other along.
For all 3 races I used a level 31 Bob with a blue up arrow.
Also, these seasonals are a good way to grind for suits and helmets with little to no input, if you choose the right cars. For comfortable wins on the first two events, a Spoon CR-Z tuned to 400pp wins with no prompting whatsoever with a level 31 Bob. Likewise for the second event I used a Citroen Xsara Rally Car '99 tuned to 497pp, which again wins with no prompting.
EDIT: I just ran the final race again in a Chaparral 2J Race Car '70 and it was a cake walk. The car was stock at 649pp and it took the lead on the 3rd lap and won by a country mile. I may have lucked out though as the lead AI car was a GT by Citroen Race Car and there wasn't a Ford GT or Zonda LM Race Car in the field.