>>30
There are motion search aided framerate conversion techniques that allow for serviceable NTSC -> PAL conversions without speed changes.
On the other hand, I'm from the school of thought that playback equipment should just support all the applicable framerates, since it's very easy for screens to do so (most in fact do without even trying: if you feed them a PAL signal with NTSC resolution and timing, also known as a
PAL60¹ signal, most TV sets just display it correctly, even analog ones made a lot of years ago).
¹
PAL60 signals are the result of
lazy as fuck or
retarded as fuck video game programmers. See also
16% slowdown which was typical in the old ages, and
epileptic judder which can be appreciated on most moder first party Nintendo games, which just discard one of every six frames (the fact that this works nicely should also give you a hint about how much time these games spend on game logic, as opposed to rendering. Remember the
GameCube 1.5, also known as
Wii, can't run multiple threads at once.)