PAL X-Box consoles can be set to 50/60hz via the MS dash. Most programs take their cue from that instead of offering the setting to the user. I don't think Surreal has an menu option for it (I gather it's not an X-Port port).
Older TVs don't always support the higher refresh rate, so 50hz is the default. That is to say, just because a signal is 60hz, doesn't mean it's not a PAL signal... NTSC (used in Japan/America) just happens not to have a 50hz setting.
Note also that PAL supports a larger resolution and colour depth range, though a PAL TV won't always support NTSC colours and vice versa... A decent TV these days will handle whatever you throw at it, making the whole issue moot.
If you boot your console with an Enigmah disc you can change it to NTSC (hence forcing 60hz no matter what). It's dead easy to change back if you find your TV won't co-operate (no "invisible menus" to try to browse through, it's just one controller button for PAL and one for NTSC).
But, the real question isn't the hertz rate... It's the frame rate. The amount of frames per second is what'll typically define the game speed; that goes up and down depending on the demands of what's happening on the screen. The hz rate is merely the rate at which the frames are sent to the TV...
Some games will "cap" the frame rate (fps) to prevent it going above the refresh rate (hz)... But I have difficulty believing the N64 is capable of a stable 60fps while playing the likes of, say, Perfect Dark, let alone that the X-Box
can pull it off during N64 emulation...
Granted Perfect Dark is an extreme example... But you get the idea.
@ganjatron: I'd assume the US versions of the game don't have the European language sets.