Lavan:
Now the question is, are there any chances that it may go defective or malfunction at higher speeds?
Reed switches can fail in a few ways, mostly by becoming magnetized (usually not enough for a measurable magnetic field outside the reed switch, but enough to cause false positives/negatives), additionally forcing too much current the switch will either melt the thin metal "reed" closed or even vaporize enough of it to cause an open. The first failure mode can happen either through short term exposure to an excessively strong magnetic field or occasionally over a long period of time during normal use. If this happens it's sometimes possible to use demagnetizer tools to fix the switch, but often it's easier to replace them and not that much more expensive. The second failure mode is usually avoided through proper design practices (i.e. limiting the current going through the sensor and taking steps to prevent shorts or large induced currents), but if and when it does happen the reed switch is basically ruined.
So to answer your specific question... Yes there is a possibility that it can malfunction at higher speeds especially if the switch has been part of a device that has previously been used a lot, due to a low level of magnetization that might have developed in the switch. On the other hand, it's by no means certain to happen and the probability really depends on the confluence of factors specific to the switch and application.