From my understanding of things, you'll get better all-around performance with the estoril. But you'll get a higher top speed with the boss or 6p (sacrificing a little acceleration for it).
If you're going for performance that is even through the powerband, I would say estoril.
If you're going for great top speed, I'd say go boss. Forget the 6p. It's too expensive for what you're getting, and the boss isn't going to give you much different results than the 6p.
I run a boss on my stock maxi cylinder with a 15mm bing. I wish I had better low end. But with a polini, it should pull well at the low end even with a boss.
So it's your choice between top end or all around goodness. Or it's your choice between like $60 (boss) and like $140 (estoril).
Wait, plus consider that you're going to have difficulty clearing the pedals with the estoril...
Save $80 or more and get the boss. You'll be fine, and won't regret it.
Or so that is my stream of consciousness for the night. Yesss.