The stock Torque physics work quite well for basic applications, you only need PhysX or Bullet, if you want to do more complicated physics simulations.
Regarding performance I would not worry so much, your biggest issue will be to get it running and fixing bugs.
To me it is an easy decission, I would chose Bullet over PhysX, since Bullet is open source and PhysX is proprietary. To install PhysX you need to register at Nvidia and request the PhysX package etc and if it does not work, you cannot do much, with Bullet you are independend and got the source code, so you can better fix bugs yourself.
Gostei da sua percepção, meu caro amigo. Muito obrigado!
Vou trabalhar com Bullet e conhecer ele mais à fundo!
You helped me a lot, I really needed those words.