The Gillet Vertigo is quite simply bizzare.
With max (35/60) DF, no turbo gives me 695pp, stage also gives 695 yet stage 3 gives only 693pp.
With stock DF (20/45), no turbo to stage 3 does as the OP states (664 vs 650), and stage 2 sits at 660pp.
With minimum (15/30) DF, however, it goes 637/639/642 with the increasing turbo level.
You may notice a suprising drop in PP from max to minimum DF levels, which is another point. At stock DF (20/45) and no turbo, adding on 1 rear DF gives 2pp extra, whilst giving it either turbo upgrades and putting on 1 extra rear DF yields a full 3pp extra. This large increase carries on until almost maximum rear DF level, varying between a 2 and a 5 pp increase (stage 3 turbo).
Setting no turbo and decreasingrear DF from the standard does not do anything extreme barring the first decrease.
Also, with stock DF and a stage 3 turbo (650pp), 1-3kg of balast reduces pp down to 649, yet from 4-59kg of balast the pp rises to a max of 660pp, and then falls as it should to 655pp at 119-133KG of blast (still higher than with no balast at all) and then increases AGAIN up to the maximum of 200kg of balast, sitting at 657pp.
A stage 2 turbo will yield a simmilarly erratic change of pp, ending up at 656pp with 200kg of bias.
Yet have no turbo installed and the pp will decrease, as it should, to 655pp.
Thats not all, either. Yes, the power limiter is also broken.
Stock DF/no turbo: pp increases as power is decreased until around 86.7%/676pp , where it starts to fall finishig at 623pp.
Stock DF/Stage 2 turbo: Same pattern as above, peaks at 82.8%/676pp, finishes at 625pp.
Stock DF/Stage3 turbo: Same again (barring a slight decrease with for the first couple of %), peaking at 81.6%/676pp and finishing at 627pp.
A simmilar rise-then-fall occurs at maximum DF.
At minimum... oh dear, it decides to take a fall-spike-fall approach.
Either the Vertigo is bugged or whatever formula PD use for PP is seriously messed up by something unique(?) to the Vertigo.