All big games on market are written with C++ these days
because of the object orientation.
Of course a Pentium 133 is too slow for this games, but every
"normal" computer (1GHz+) with a good graphics card ist OK,
because the graphics card makes much of the graphical work
in hardware.
You dont get a "Noticable speed decrease" if your game is designed
correctly.
If you didnt code correctly, game speed slows down also if you
dont use OOP.
I´ve heared people saying PB is slow on displaying 1 sprite,
where you can display 500 smoothly.
Go with OOP, you´ll see its much better to maintain and to read -
especially in big projects.