no it still should be but it's timings will be off from what they were factory placed at, like lets say your kingston ram is 8-8-8-10 and the gskill is for instance 6-7-7-9, it would by default switch to a 8-8-8-10. But if you were to buy that gskill ram wihtout OCing the kingston, the gskill ram would default to 1333 speed and the default timings of the slowest speed stick (the kingston).
I don't know if it's on sale still or not but gskill 8gb (2x4 kit) was $50 dollars on newegg.