When I overclock my Raspberry Pi B+ to 1200 MHz, it spits out a nasty kernel panic, even though it is overvolted and cooled sufficiently. However, on my Raspberry Pi Model B, I have gone past 1.3 GHz. What is the problem here?
The problem is a lack of understanding on your part.
If overclocking works its is a bonus. There are no guarantees.
It depends on the luck of the draw as to whether the silicon you actually have is good enough to overclock to any particular value.