Slowdown when accessing data at page boundaries?
Go to Agner manuals page and download them all, you will find tons of interesting info there. In particular, microarchitecture.pdf says 


  There is a false dependence between memory addresses with the same set and offset, i.e. with a distance that is a multiple of 4 Kbytes:


;Example 9.6. Sandy bridge false memory dependence
mov [rsi],eax
mov ebx,[rsi+1000H] ;False memory dependence


I.e. the access becomes slower because cpu thinks that it may be the same address, so the load in the second line may depend on the store in the first line and thus cpu serializes execution of these operations.

AFAIR, it wasn't changed in latest Intel cpus.